feat(sources)!: add custom auth strategy for components with HTTP server

[esensar]

Summary

This adds custom auth strategy for components with HTTP server (http_server, datadog_agent, opentelemetry, prometheus) besides the default basic auth. This is a breaking change because strategy is now required for auth - for existing configurations strategy: "basic" needs to be added.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

Besides the tests added to the codebase, I ran basic tests with http_server source component:

sources:
  http_server_source:
    type: "http_server"
    address: "0.0.0.0:80"
    auth:
      strategy: "custom"
      source: |-
        .headers.authorization == "test"

sinks:
  console:
    inputs: ["http_server_source"]
    target: "stdout"
    type: "console"
    acknowledgements:
      enabled: false
    encoding:
      codec: "json"

Tested by making calls via curl:

$ curl -X POST vector:80
{"code":401,"message":"Auth failed"}
$ curl -X POST vector:80 -H "Authorization: test"

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

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References

Related: #22213

[esensar]

I have made this a breaking change, requiring explicit strategy, for consistency (I have had a similar situation in a previous contribution: #19892 (comment)). Let me know if you want me to add untagged for serde deserialization, to make this a non-breaking change.

[estherk15]

Suggested change

	HTTP authentication should be used with HTTPS only, as the authentication credentials are passed as an
	HTTP header without any additional encryption beyond what is provided by the transport itself.
	Use the HTTP authentication with HTTPS only. The authentication credentials are passed as an
	HTTP header without any additional encryption beyond what is provided by the transport itself.

[estherk15]

Suggested change

	The username and password are concatenated and encoded via [base64][base64].
	The username and password are concatenated and encoded using [base64][base64].