chore(config): consolidate schema metadata application

[pront]

Summary

Consolidates configurable schema metadata application without changing generated schema output.

• replaces apply_base_metadata with the unified apply_metadata entry point across generated and handwritten schema code
• decomposes schema metadata, custom attribute, and validation application into focused helpers while preserving their original ordering and behavior
• removes redundant field-level title/description clearing from derive-macro output; those calls operated on a freshly defaulted Metadata
• updates enum variant and handwritten schema call sites to use the consolidated entry point

Metadata::merge semantics remain unchanged, and regenerated component documentation has no net diff.

Vector configuration

N/A — this refactors schema generation internals and does not change Vector configuration syntax.

How did you test this PR?

On the latest origin/master:

• make generate-docs
• make check-generated-docs
• cargo test -p vector-config
• make check-clippy
• make check-fmt
• git diff origin/master...HEAD --check

Change Type

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

Is this a breaking change?

• Yes
• No

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.

References

#14263 — Annotate configurable types to describe their input format
#15001 — Improve generated-doc handling of schema annotations

#16366 — Fix base vs. override schema metadata handling
#15906 — Combine field and type metadata for optional fields

[datadog-vectordotdev]

 

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🧪 All tests passed
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