Change default for Runner Feature flag `FF_GIT_URLS_WITHOUT_TOKENS` to `true`

Overview

To limit the potential of token leakage, we want to switch the FF's default to true.

This is a potential breaking change for a subset of configurations, thus we want to do that on the next major release.

Additional notes and references

1. This issue is the implementation issue.
2. The related deprecation notice is Deprecation - Remove hard coded credentials fro... (gitlab#518709 - closed) • Hannes Hörl, Darren Eastman • 17.9
   • With !5430 (merged) this is not a breaking change anymore