Review version validation code

[charith-elastic]

Things to address here are:

• Find a way to have supported versions defined in a single place. Elasticsearch supported versions are in pkg/controller/elasticsearch/version whereas the other resources have their supported versions defined in pkg/controller/common/version. The advantage of having all supported versions declared in a single place is that it leaves less room for errors when updating the upper and lower bounds as the Stack evolves.
• Current checks do not allow version downgrades even at the patch level (e.g. going from 7.6.1 to 7.6.0 is not allowed). I don't think there's a good reason for this as semver principles do allow it.
• Consider whether we want to implement the support matrix.
• Consider whether we want to enforce the upgrade order in the webhook.

Follow-up from #2781