[FEATURE] Make flagd independent of go sdk provider

[Kavindu-Dodan]

Requirements

Right now our e2e tests rely on go sdk provider to execute e2e tests. Given these test definitions are located under flagd, go.mod will have a dependency on the go provider. This creates a circular dependency between flagd & flagd go provider

graph TD;
    flagd --> go-sdk-provider;
   go-sdk-provider -->  flagd;

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We need to remove this dependency by ideally isolating e2e tests to dedicated package so that flagd go.mod becomes isolated.

[Kavindu-Dodan]

There's a direct dependency from integration tests to go flagd provider. Given flagd provider internally use flagd core, this creates a circular dependency that's harder to resolve. Further, given that we use a go workspace, it's impossible to maintain e2e tests only dependencies locally.