Reactivate the Pebble extension

[chkal]

This extension is currently disabled, because the underlying template engine doesn't support the new jakarta.* package namespace yet. We have to:

• Wait for a new version of the template engine and update our dependencies.
• Reactivate the corresponding tests in our testsuite (currently disabled via @Ignore)

As a last resort we may also decide to remove the extension.

Please note that I assigned this issue to the 2.0.0 milestone. However, the issue should NOT be a blocker for the 2.0.0 release.

[chkal]

I created a corresponding issue in the upstream project: PebbleTemplates/pebble#548

[chkal]

Upstream pull request: PebbleTemplates/pebble#549

[chkal]

Upstream issue fixed. So we just have to wait for the next release, so we can use the new Servlet5Loader. Currently, the version in the pom.xml is set to 3.1.5-SNAPSHOT. So 3.1.5 should work.

[erdlet]

3.1.5 was released in february, so we can update and test the extension now.