rel: prep release v1.5.2

[JamieDanielson]

Which problem is this PR solving?

• release prep for v1.5.2

Short description of the changes

• update releasing doc for how to find proto version in otel java, and how to update in tests
• update version in root build.gradle to 1.5.2
• update otel version to 1.27.0 and proto version to 0.20.0 in distrometadata
• update changelog for v1.5.2
• update readme with otel versions 1.27.0
• update test with new proto version

A docs PR has been prepped with the new release version, to be merged once this release is out.