Lower Geo concurrency default settings

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What does this MR do and why?

Caution

This MR was somehow affected by weird pipeline issues. The pipeline, stemming from gitlab-community, always failed. Though when raising an MR directly via gitlab-org, it was successful with the exact same changes. We therefore shipped the changes via !186326 (closed).

Currently investigating the possible CI performance leaks...

Pipeline performance leaks were fixed.

This MR lowers the Geo-related concurrency default settings as outlined in #24081 (closed). By lowering the concurrency default values, smaller environments will profit from a more balanced resource utilization. Larger deployments most likely will have to further tweak those options to avoid replication lag.

As suggested in #24081 (closed), the docs changes are handled in a separate MR (see !184510 (merged)).

Notes:

• The issue also mentions files_max_capacity but its default value is already set to 10

TODO:

• Migration spec tests?
• Tuning docs?
• Add columns_changing_default?
• Changelog?

🔧 with at Adfinis

References

• #24081 (closed)
• !184510 (merged)
• (#393570)

Screenshots or screen recordings

n/a

How to set up and validate locally

At least run the newly defined spec tests:

bundle exec rspec spec/migrations/db/migrate/20250312124044_change_geo_performance_default_settings_spec.rb

MR acceptance checklist

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