Respect .spec.upgradeConstraintPolicy

[m1kola]

Please read RFC for better formatting and full scope. The excerpt below is just to indicate the scope covered by this specific issue.

Need to update code to respect .spec.upgradeConstraintPolicy accordingly to the RFC:

When .spec.upgradeConstraintPolicy is set to Ignore we do not apply upgrade constraints. This means an Operator can be transitioned to any available version of the package (even one older than the currently installed one). Note that, if set, other constraints on Operator still apply (e.g. .spec.version and .spec.channel).

When .spec.upgradeConstraintPolicy is set to Enforce we use either semver or legacy semantics depending on the position of the ForceSemverUpgradeConstraints feature gate.

[m1kola]

We probably need to do #437 first because with the current structure of variable sources it is tricky to get access to relevant Operator.

[m1kola]

We need to update tests introduced in #472 to include a case where we make sure that it is possible to upgrade within major version zero when .spec.upgradeConstraintPolicy is set to Ignore as this is the only way to upgrade in these versions.

For example, upgrade from 0.0.1 to 0.0.2 is not possible without this.

[m1kola]

I will either need #437 to be solved (PRs #498, #499, #500 and #501 to get merged) or #508 to get merged to be able to make progress with this.