chore(*) remove Go module for the changelog generator

[jpeach]

Summary

Remove the Go module for the changelog generator and hoist its
dependencies up into the root module. Fix all the new lint warnings,
since the linter wasn't running on the nested module.

Full changelog

N/A

Issues resolved

Updates #2200.

Documentation

N/A

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Add backport-to-stable label if the code is backwards compatible. Otherwise, list breaking changes.

[codecov-commenter]

Codecov Report

Merging #2328 (1c159a7) into master (91e9477) will increase coverage by 0.23%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2328      +/-   ##
==========================================
+ Coverage   50.70%   50.93%   +0.23%     
==========================================
  Files         871      879       +8     
  Lines       40631    40761     +130     
==========================================
+ Hits        20601    20762     +161     
+ Misses      18034    17976      -58     
- Partials     1996     2023      +27     

Impacted Files	Coverage Δ
tools/releases/changelog/generator.go	0.00% <0.00%> (ø)
tools/releases/changelog/main.go	0.00% <0.00%> (ø)
tools/releases/changelog/root.go	8.16% <0.00%> (ø)
tools/releases/changelog/utils.go	0.00% <ø> (ø)
pkg/xds/generator/direct_access_proxy_generator.go	80.26% <0.00%> (-1.32%)	⬇️
api/internal/util/proto/types.go	100.00% <0.00%> (ø)
...k8s/native/controllers/proxytemplate_controller.go	0.00% <0.00%> (ø)
...kg/plugins/resources/k8s/native/pkg/test/within.go	100.00% <0.00%> (ø)
api/internal/util/proto/proto.go	62.50% <0.00%> (ø)
... and 14 more

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[bartsmykla]

lgtm