Fixes #6690, #6933 - google-secret-manager extend coverage and native

[JiriOndrusek]

fixes #6690
fixes #6933

Google-secret-manager native support is added:

• tech preview status is changed to stable
• extension and tests are moved from JVM modules into standard one
• native support requires duplication of some code (which is already present in google-pubsub). The refactor is not part of this PR (as it would make the whole change more complicated). I created a ticket Google-secret-manager and google-pubsub: create a common extension support #6934 to do such refactor in the future.

Test coverage is added:

• the real backend is required (as was before)
• pubsub test resource had to be added to simulate the sending of the message to the secret refresh topic (see more details in the comment of GoogleSecretManagerTest class)

[jamesnetherton]

Please rebase as main just got bumped to 3.19.0-SNAPSHOT. You'll need to update the 'native since' property to 3.19.0.

The refactor is not part of this PR (as it would make the whole change more complicated)

That's fine, but we should aim to get #6934 done ASAP. We can't have the potential for duplicate substitutions on the classpath.

[JiriOndrusek]

I'll rebase right now and will start working on #6934 during today, if needed I can prepare the fix as a second commit to this PR