Move bnd.bnd file configuration into 'bnd' element of bnd-maven-plugin

[HannesWell]

Description

As discussed in https://github.com/google/gson/pull/2711, this moves the content of the bnd.bnd file into a bnd configuration element of the bnd-maven-plugin.

Checklist

• [x] New code follows the Google Java Style Guide\ This is automatically checked by mvn verify, but can also be checked on its own using mvn spotless:check.\ Style violations can be fixed using mvn spotless:apply; this can be done in a separate commit to verify that it did not cause undesired changes.
• [ ] If necessary, new public API validates arguments, for example rejects null
• [ ] New public API has Javadoc
  • [ ] Javadoc uses @since $next-version$
    ($next-version$ is a special placeholder which is automatically replaced during release)
• [ ] If necessary, new unit tests have been added
  • [ ] Assertions in unit tests use Truth, see existing tests
  • [ ] No JUnit 3 features are used (such as extending class TestCase)
  • [ ] If this pull request fixes a bug, a new test was added for a situation which failed previously and is now fixed
• [ ] mvn clean verify javadoc:jar passes without errors

[HannesWell]

Your welcome. Thanks for the fast response.