Avoid cross-dependencies between components

[ghost]

Currently some components of Vector import and use code from other components. The list of such dependencies is the following:

• sources-kubernetes depends on sources-file, transforms-json_parser, transforms-regex_parser;
• sources-syslog depends on sources-socket;
• sources-vector depends on sources-socket;
• sinks-humio_logs depends on sinks-splunk_hec;
• sinks-new_relic_logs dependes on sinks-http;
• sinks-sematext_logs depends on sinks-elasticsearch.

I think in long term this might make it harder to refactor individual components, as change is one component might break some other (seemingly) unrelated component. So ideally we need to identify the common code and factor it out to lib crates or, if the code is too specific, at least as util modules.

The above relates only to implementation of components, but not to their tests. Using other components in tests I think is less an issue, although some tests for components might be changed to not depend on other components. In particular, I think most of the tests depending on json_parser can be modified to avoid such a dependency.

See also #1924.

[ktff]

These have already been resolved:

• syslog source
• vector source
• honeycomb sink
• papertrail sink

• although some of their feature dependency can be updated to reflect this. chore: Remove unneeded cross feature dependency #3210

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kubernetes_logs source uses transforms:

• merge whole so there is little to be gained in separating common code.
• regex partially so there is common code that could be extracted, although it would be quite specific.
  • To extract common regex or not? (EDIT: No, I don't see any clean way of separating shared code from it )
• json_parser partially so there is common code to be extracted, and it's something that can be shared, even specialized since tests use it in a same/similar way as kuberentes_logs source.
  • Extract chore: Remove dependency on transforms-json_parser #3214

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Others:

• humio_logs sink uses whole splunk_hec sink
• new_relic_logs sink uses whole http sink
• sematext_logs sink uses whole elasticsearch sink

They are using whole of the other sink, as they are basically wrappers with some extra/default configuration. Their common code would be the whole sink so I think we wouldn't gain much.

cc. @binarylogic