✨Add support for clusterctl gitlab auth

[MaxRink]

What this PR does / why we need it:
This PR adds support in clusterctl for gitlab instances that require auth.
Which issue(s) this PR fixes
Fixes # n/a

/area clusterctl

[k8s-ci-robot]

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[k8s-ci-robot]

@MaxRink: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-apidiff-main	7b1ee0f	link	false	/test pull-cluster-api-apidiff-main

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[chrischdi]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 7b5f06718de23cb19494e5fdd45ddc9c9f808fe5

[MaxRink]

@chrischdi The failing CI technically is a breaking API change.
I /could/ probably avoid it by not passing ctx and instead using ctx.background() but that would leave the gitlab implementation inconsistent with GitHub

[chrischdi]

I think that change is okay as long as we do not cherry-pick this to an older release.

[chrischdi]

Note we ~ did the same change for NewGithubRepository at this PR:

• ⚠️ Improve Context handling in clusterctl #8939

[sbueringer]

We're good

https://github.com/kubernetes-sigs/cluster-api/tree/main/cmd/clusterctl#compatibility-notice

When this package is used as a library, we do not currently provide any compatibility guarantees. We will make reasonable efforts to follow a typical deprecation period prior to removal, but breaking changes can happen when necessary.