Add a mechanism to patch provider configuration post enrollment

[jhrozek]

This is a follow-up to issue #3263. In addition to storing the provider configuration on provider creation we'll also want to patch the provider configuration after the fact. We might want to implement something like:

message ProviderPatch {
	// to allow generic configuration changes. 
	google.protobuf.Struct config = 1;
}

message PatchProviderRequest {
	Context context = 1;
	ProviderPatch = 2;

	google.protobuf.FieldMask update_mask = 3;
}

message PatchProviderResponse {
	Provider provider = 1;
}

rpc PatchProvider(PatchProviderRequest) returns (PatchProviderResponse) {
	option (google.api.http) {
		patch: "/api/v1/provider"
		body: "patch"
	}
	option (rpc_options) = {
		target_resource = TARGET_RESOURCE_PROJECT;
		relation = RELATION_PROVIDER_UPDATE;
	}
}

and expose that through the CLI. To implement the patch handler we'll need to:

• Extend the ProviderManager interface with a new PatchProvider method, e.g PatchProvider(ctx context.Context, uuid uuid.UUID, patch minderv1.ProviderPatch) (minderv1.Provider, error)
• Extend the ProviderClassManager interface with a new Patch method
• The ProviderManager.PatchProvider would get the correct class manager and call its Patch
• The per-provider Patch implementation is where the generic protobuf struct is unmarshalled into the correct Go struct and the configuration adjusted

[jhrozek]

Co-assigning @blkt who will be working on this issue to get it out of draft and merged as I'm away tomorrow and Friday.