Update badger to latest version

[kruskall]

We are using an older badger version that is no longer supported. We should switch to the newer/latest version (currently v4)

[axw]

When we're ready for this, we should revive https://github.com/elastic/apm-server/pull/11344 and replace/update the GC test.

[carsonip]

This needs to be tested thoroughly, as my experiments show that the memory profiles (v2 vs v4) look quite different:

v2: https://github.com/carsonip/tbs-badger-playground/tree/main/prefetch v4: https://github.com/carsonip/tbs-badger-playground/tree/badgerv4/prefetch