Added a join slack badge in CAPA repo for k8s cluster-api-aws channel

[shivi28]

What type of PR is this?
/kind feature

This PR adds a join slack badge in CAPA repo for k8s cluster-api-aws channel.

Now we can see badge in CAPA repository.

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:

Checklist:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

Release note:

Added a join slack badge in CAPA repo Readme.md

[k8s-ci-robot]

@shivi28: This issue is currently awaiting triage.

If CAPA/CAPI contributors determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

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[Ankitasw]

/lgtm

[sedefsavas]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sedefsavas

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