Add Deployment planners documentation

[sudo87]

This PR adds documentation related to Deployment Planners in CloudStack.

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📚 Documentation preview 📚: https://cloudstack-documentation--594.org.readthedocs.build/en/594/

[sudo87]

@blueoragnutan docbuild

[sudo87]

@harikrishna-patnala please review this pr

[prashanthr2]

I would suggest replacing.

Deployment planners determine how and where instances are placed across clusters within a zone with Deployment planners determine how instances are allocated within a zone based on configuration settings.

As deployment planner itself can work at the pod level and also the actual deployment is on particular host. I think it is better to just say zone.

Except that everything else lgtm

[rajujith]

@prashanthr2 based on my discussion with @sudo87 offline, we decided the retain the original statement as it's the correct one as per the functionality.

[rajujith]

@blueoragnutan docbuild

[sudo87]

@blueoragnutan docbuild

[sureshanaparti]

@sudo87 can you target to 4.22 branch?

[sudo87]

@sudo87 can you target to 4.22 branch?

Sure @sureshanaparti, please review and merge.