Doc about preemptible VM instance

[sayantani11]

What type of PR is this?

What this PR does / why we need it:
To implement preemptible VM instance with the use of CAPG.

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

Special notes for your reviewer:
Once we add Machine pool templates we need to add the template in this doc as well

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Preemptible VM documentation

[k8s-ci-robot]

Hi @sayantani11. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[sayantani11]

#451

[shivanshuraj1333]

/label tide/merge-method-squash

[cpanato]

/ok-to-test

[cpanato]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato

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