upgrade staging instance to 15.4

The current version is 15.0 with the operator v0.8.0.

The instance should be upgraded to the operator v0.12.2 and gitlab 15.5.2 (https://docs.gitlab.com/ce/update/#upgrade-paths) According the upgrade path allowed: 15.0.Z -> 15.4.0 -> latest 15.Y.Z

We are starting for the 15.0.0 version so the upgrade process must be:

• upgrade operator to 0.12.0 / chart version 6.4.0 (gitlab 15.4.0)
• upgrade operator to 0.12.2 / chart version 6.4.2 (gitlab 15.4.2)

It seems there are no breaking changes between those operator versions

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Migrated from T4610 (view on Phabricator)