[v1.15] Fix dead links and make minor cleanups in documentation

[mflendrich]

This PR is a cherry-pick of #2499 into the v1.15 release branch.

Resolves #2502

/kind documentation

[scylla-operator-bot]

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

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-gke-release-script-latest	19fa9f8	link	true	/test e2e-gke-release-script-latest
ci/prow/e2e-gke-parallel-clusterip	19fa9f8	link	true	/test e2e-gke-parallel-clusterip
ci/prow/e2e-gke-parallel	19fa9f8	link	true	/test e2e-gke-parallel
ci/prow/e2e-gke-serial	19fa9f8	link	true	/test e2e-gke-serial
ci/prow/e2e-gke-multi-datacenter-parallel	19fa9f8	link	true	/test e2e-gke-multi-datacenter-parallel
ci/prow/images	19fa9f8	link	true	/test images
ci/prow/docs-multiversion	19fa9f8	link	false	/test docs-multiversion

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[zimnx]

Please rename PR title, we want it to describe what it brings. PR titles are part of autogenerated release notes, so it's easier to understand when it describe changes.

For backports we used to add [v1.15] prefix to distinguish those landing on non-default branch.

[mflendrich]

@zimnx this is done, please look again

[zimnx]

thanks!
/lgtm

[scylla-operator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mflendrich, zimnx

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