Refactor deployment handler

[sameerzuberi]

Issue #, if available:

Description of changes:
Significant refactor of deployment_handler

• Removed configuration logic from deployment handler and condensed it in deployment_configuration. We now have two generic helper functions to read Nucleus and system configs and one helper function to retrieve the posix user (this is because the posix user is under an additional nested key)
• Removed dependency resolution logic from deployment handler and created dependency_resolver. Also refactored dependency resolution in the process to reduce repeated code and improve readability.
• Created dataplane_manager to handle all cloud calls made during the deployment workflow.

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