📖 Update CAPI support and guarantees for v1.9

[chandankumar4]

What this PR does / why we need it:

• This PR updates the supported versions for the release cycle (1.9).

@kubernetes-sigs/cluster-api-release-team

/area documentation

[k8s-ci-robot]

Hi @chandankumar4. Thanks for your PR.

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[fabriziopandini]

/lgtm
only note from my side:

There are two half on this PR

• Drop 1.5 column, mark 1.6 version as EOL
• Add 1.9 column

The first half has to be back ported to the release-1.8 branch, the second no.
I'm not sure how this has been done in the past, but please keep it in mind for the backport

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: d5e91cb4c63e42e95580b7f86fa1d9dc3d0af228

[fabriziopandini]

/ok-to-test

[fabriziopandini]

/hold

This seems a duplicate of #11151
cc @Sunnatillo

[fabriziopandini]

/hold cancel

[fabriziopandini]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

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[fabriziopandini]

@chandankumar4 could you kindly open the manual cherry pick as per #11163 (review)?

[sbueringer]

Usually we don't add information about v1.9 to the v1.8 book. Or do you mean only cherry-pick a subset of this PR?

[fabriziopandini]

I have raised the same question in #11163 (review), proposing a manual cherry pick that we need as soon as possible (1.6 is EOS from ~1m now, and the book still reports it as supported).
cc @Sunnatillo

[sbueringer]

Ah my bad, missed that comment. Makes sense!

[chandankumar4]

Have raised the manual cherry-pick PR #11177
@fabriziopandini

[Sunnatillo]

Part of #11092