docs(README): update clients-config.json snippet

[antoineauger]

This MR fixes some typos for the clients-config.json snippet in README.md (and the e2e config).
As is, the clients-config.json snippet is invalid and/or the server returns a 500 Internal Server error:

Server logs

[15:06:39 Error] Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware
An unhandled exception has occurred while executing the request.
System.Text.Json.JsonException: ''' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 1.
---> System.Text.Json.JsonReaderException: ''' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 1.
 at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes)
 at System.Text.Json.Utf8JsonReader.ConsumeValue(Byte marker)
 at System.Text.Json.Utf8JsonReader.ReadSingleSegment()
 at System.Text.Json.Utf8JsonReader.Read()
 at System.Text.Json.Utf8JsonReader.TrySkip()
 at System.Text.Json.JsonDocument.TryParseValue(Utf8JsonReader& reader, JsonDocument& document, Boolean shouldThrow, Boolean useArrayPools)
 at System.Text.Json.Serialization.Converters.JsonElementConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)
 at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
 at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
 --- End of inner exception stack trace ---
 at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, JsonReaderException ex)
 at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
 at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo jsonTypeInfo, Nullable`1 actualByteCount)
 at System.Text.Json.JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan`1 json, JsonTypeInfo jsonTypeInfo)
 at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
 at Duende.IdentityServer.Extensions.TokenExtensions.AddObject(Claim claim) in /_/src/IdentityServer/Extensions/TokenExtensions.cs:line 158
 at Duende.IdentityServer.Extensions.TokenExtensions.CreateJwtPayloadDictionary(Token token, IdentityServerOptions options, ISystemClock clock, ILogger logger) in /_/src/IdentityServer/Extensions/TokenExtensions.cs:line 112
 at Duende.IdentityServer.Services.DefaultTokenCreationService.CreatePayloadAsync(Token token) in /_/src/IdentityServer/Services/Default/DefaultTokenCreationService.cs:line 87
 at Duende.IdentityServer.Services.DefaultTokenCreationService.CreateTokenAsync(Token token) in /_/src/IdentityServer/Services/Default/DefaultTokenCreationService.cs:line 74
 at Duende.IdentityServer.Services.DefaultTokenService.CreateSecurityTokenAsync(Token token) in /_/src/IdentityServer/Services/Default/DefaultTokenService.cs:line 275
 at Duende.IdentityServer.ResponseHandling.TokenResponseGenerator.CreateAccessTokenAsync(ValidatedTokenRequest request) in /_/src/IdentityServer/ResponseHandling/Default/TokenResponseGenerator.cs:line 494
 at Duende.IdentityServer.ResponseHandling.TokenResponseGenerator.ProcessTokenRequestAsync(TokenRequestValidationResult validationResult) in /_/src/IdentityServer/ResponseHandling/Default/TokenResponseGenerator.cs:line 393
 at Duende.IdentityServer.ResponseHandling.TokenResponseGenerator.ProcessAsync(TokenRequestValidationResult request) in /_/src/IdentityServer/ResponseHandling/Default/TokenResponseGenerator.cs:line 96
 at Duende.IdentityServer.Endpoints.TokenEndpoint.ProcessTokenRequestAsync(HttpContext context) in /_/src/IdentityServer/Endpoints/TokenEndpoint.cs:line 110
 at Duende.IdentityServer.Endpoints.TokenEndpoint.ProcessAsync(HttpContext context) in /_/src/IdentityServer/Endpoints/TokenEndpoint.cs:line 76
 at Duende.IdentityServer.Hosting.IdentityServerMiddleware.Invoke(HttpContext context, IEndpointRouter router, IUserSession userSession, IEventService events, IIssuerNameService issuerNameService, ISessionCoordinationService sessionCoordinationService) in /_/src/IdentityServer/Hosting/IdentityServerMiddleware.cs:line 98
 at Duende.IdentityServer.Hosting.IdentityServerMiddleware.Invoke(HttpContext context, IEndpointRouter router, IUserSession userSession, IEventService events, IIssuerNameService issuerNameService, ISessionCoordinationService sessionCoordinationService) in /_/src/IdentityServer/Hosting/IdentityServerMiddleware.cs:line 113
 at Duende.IdentityServer.Hosting.MutualTlsEndpointMiddleware.Invoke(HttpContext context, IAuthenticationSchemeProvider schemes) in /_/src/IdentityServer/Hosting/MutualTlsEndpointMiddleware.cs:line 94
 at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
 at Duende.IdentityServer.Hosting.DynamicProviders.DynamicSchemeAuthenticationMiddleware.Invoke(HttpContext context) in /_/src/IdentityServer/Hosting/DynamicProviders/DynamicSchemes/DynamicSchemeAuthenticationMiddleware.cs:line 47
 at Duende.IdentityServer.Hosting.BaseUrlMiddleware.Invoke(HttpContext context) in /_/src/IdentityServer/Hosting/BaseUrlMiddleware.cs:line 27
 at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

This was a leftover after #115.
e2e/config/clients.json was correctly updated back then.

🛠️ with ❤️ by Siemens

[AleF83]

Thanks for contributing!