[BUG] Optimize focus-container validation to opt-in

[EdDev]

Describe the bug
Currently, the new focus-container rule is by default included and requires an opt-out to be suppressed.

This has the potential of breaking some projects workflow, where the commonly used target is including the linter together with other actions (e.g. build, unit tests).

An example of such a workflow can be seen in the kubevirt project [1].

[1] kubevirt/kubevirt#10136

Expected behavior
Do not enforce this focus-container rule by default, allow the users to opt-in for it.