🌱 Clean up kube version parsing

[CecileRobertMichon]

What this PR does / why we need it: Currently version parsing in CAPI is inconsistent and there is duplicate constants for regex expression. Also, KCP webhooks (kubeadm/controlplane/api) import the util package to use the version parsing helper and kubeSemver which means the util package is unable import the KCP api (it already imports the core API) as it causes dependency cycles. This PR moves the version logic to a new util/version package and deprecates the func in the util package, as well as reuses the same kubeSemver var across all uses in the code. It also makes the difference between "tolerant" semver parsing (with or without "v" prefix) and not ("v" prefix required), which otherwise is easy to miss as it's a 1 char difference in the regex. There are no behavior/functional changes as part of this PR.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Partially addresses #3697

[fabriziopandini]

linking this issues because related #3697

[vincepri]

/milestone v0.4.0

[vincepri]

Overall great work, thanks @CecileRobertMichon for tackling this!

[CecileRobertMichon]

Thanks for linking #3697 @fabriziopandini, I knew there was an issue for this but I had lost it... I think we should merge this refactor first which doesn't make any changes to validation then make any necessary changes separately so we don't mix refactoring and validation changes.

[vincepri]

/lgtm

[CecileRobertMichon]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [CecileRobertMichon]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment