chore: configure release-please for example pom.xml

[stenalpjolly]

Summary

Configures Release Please to automatically track and synchronize the mcp-toolbox-sdk-java dependency version in example/pom.xml during release generation by adding it to extra-files and annotating the dependency with the x-version-update inline marker.

Expectation & Implementation

• Problem: During automated release PR generation, Release Please increments the root SDK version in pom.xml to the target release version. Because example/pom.xml was omitted from extra-files, its SDK dependency remained pinned to 0.3.0-SNAPSHOT. In CI presubmit workflows, step 26 (Build Example with Maven) executes cd example && mvn compile immediately following mvn install -DskipTests, triggering dependency resolution failures due to missing SNAPSHOT artifacts.
• Solution:
  1. Added <!-- {x-version-update:mcp-toolbox-sdk-java:current} --> to the com.google.cloud.mcp:mcp-toolbox-sdk-java dependency entry in example/pom.xml.
  2. Registered "example/pom.xml" under packages["."].extra-files in release-please-config.json.
  3. Release Please will now automatically scan example/pom.xml and rewrite the dependency version to match the released package version in lockstep across all release PRs.

Test cases

1. Local Build & Compilation Verification:
   • Ran JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 mvn install -DskipTests -Djacoco.skip=true to install root SDK artifacts.
   • Ran cd example && JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64 mvn compile and verified BUILD SUCCESS.
2. Presubmit CI Validation:
   • All 11 GitHub Actions presubmit checks on this branch passed cleanly, including Compile/build, Lint/lint, Google GitHub Admin: Actions Check, cla/google, and conventionalcommits.org.

Acceptance criteria

• release-please-config.json includes "example/pom.xml" under packages["."].extra-files.
• example/pom.xml contains the valid <!-- {x-version-update:mcp-toolbox-sdk-java:current} --> marker on the mcp-toolbox-sdk-java dependency.
• All GitHub Actions presubmit checks (Compile/build, Lint/lint, etc.) pass.
• Release Please successfully synchronizes example/pom.xml alongside root pom.xml during release PR generation.

Breaking changes

None. This is an internal CI and release-tooling configuration update with no changes to the SDK runtime or public API surfaces.