Migrate off of OSSRH

[jpd236]

OSSRH is being sunset: https://central.sonatype.org/news/20250326_ossrh_sunset/

We use it to publish SNAPSHOT builds, and then we have a script to push a particular SNAPSHOT directly to Maven Central as an RC. Currently there is no official Gradle support for the replacement Central Publisher Portal, though this is supposedly coming.

SNAPSHOTS are apparently possible but behave a bit differently: https://central.sonatype.org/publish/publish-portal-snapshots/#enabling-snapshot-releases-for-your-namespace. We might actually be fine with the default Gradle plugin here, though retention of snapshot builds may be a bit less (90 days vs. some longer period).

[jpd236]

https://central.sonatype.org/publish/publish-portal-ossrh-staging-api/ should allow us to migrate in-place if needed before a plugin with direct support for the new API is available.

To be done before next functional code change (to restore SNAPSHOT builds):

• Migrate the com.android namespace from OSSRH to Central Publisher at https://central.sonatype.com/. While there are some other artifacts in this namespace, I've verified with the other owners of this namespace that there are no plans to publish updates to any of those artifacts there (rather than Google's own Maven repository). This may happen automatically at some point after 6/30, but I'm not certain.
• Enable SNAPSHOT builds for the migrated project
• Obtain new auth credentials and update GitHub secret
• Update Gradle config to point to new SNAPSHOT publishing URL
• Commit change and verify successful SNAPSHOT publish

To be done before next full release:

• Update internal deploy-release-to-staging.sh script to point to new publishing URL
• Perform RC release and verify successful publishing, including new staging repository release process
• Update internal deploy.md doc with latest deployment instructions

I don't think we need to do these ahead of the 6/30 deadline as we're not actively making changes, but we'll need to do this before any future changes.