chore: v1.2.0/v0.15.0 release proposal

[aabmass]

New release following releasing.md.

Draft release notes: https://github.com/GoogleCloudPlatform/opentelemetry-operations-js/releases/edit/untagged-cff1f617afa0daf2852b

[codecov]

Codecov Report

Merging #463 (fcb3b56) into main (54e8ca4) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #463   +/-   ##
=======================================
  Coverage   94.92%   94.92%           
=======================================
  Files          13       13           
  Lines         473      473           
  Branches       91       91           
=======================================
  Hits          449      449           
  Misses         24       24           

Impacted Files	Coverage Δ
...telemetry-cloud-monitoring-exporter/src/version.ts	100.00% <100.00%> (ø)
.../opentelemetry-cloud-trace-exporter/src/version.ts	100.00% <100.00%> (ø)

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