refactor: Service Wiring / Concurrency pt 1

[dave-gray101]

This PR is the start of transitioning our core services to the core/application.go \ core/startup model.
In order to keep things reviewable, this PR will have a limited scope - rather than moving everything at once, my goal is to select services that are covered by existing tests for the detection of regressions. Therefore, this PR contains the following components:

• begins the creation of http/middleware, migrating request object handling outside the endpoints themselves.
• • also takes over some existing middleware to this new folder, for organizational reasons.
• • Does transition openai endpoints to use the common model middleware - this should help test coverage
• Finishes up service wiring infrastructure in core/startup
• pkg/concurrency - basic JobResult structure
• Port over TTS Endpoints to TextToSpeechBackendService
• Port over Embedding Endpoint to EmbeddingBackendService

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Squashing again, the middleware approach is much more sustainable.

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