Fix: Update Sonatype URL and add to snapshot workflow

The Sonatype snapshot repository URL has been updated from oss.sonatype.org to central.sonatype.com in all relevant files, including Gradle configurations and documentation.

The snapshot repository URL has also been added as an environment variable to the `publish-snapshot.yml` GitHub Actions workflow.

Author: google-labs-jules[bot]

.github/workflows/publish-snapshot.yml

@@ -29,6 +29,7 @@ jobs:
         env:
           ORG_GRADLE_PROJECT_repoUsername: ${{ secrets.SONATYPE_USERNAME }}
           ORG_GRADLE_PROJECT_repoPassword: ${{ secrets.SONATYPE_PASSWORD }}
+          ORG_GRADLE_PROJECT_snapshotRepoUrl: "https://central.sonatype.com/content/repositories/snapshots/"
           ORG_GRADLE_PROJECT_signingKey: ${{ secrets.SIGNING_KEY }}
           ORG_GRADLE_PROJECT_signingKeyId: ${{ secrets.SIGNING_KEY_ID }}
           ORG_GRADLE_PROJECT_signingPassword: ${{ secrets.SIGNING_PASSWORD }}