CSPL-2346 Upgrade Strategy for Multisite indexers

[tgarg-splunk]

Implemented the design for the multisite IDXC upgrade strategy for the Splunk Operator Level II support. Specifically:

• Updated isIndexerClusterReadyforUpgrade to check if indexers on previous sites are ready
• Added getIndexerClusterSortedSiteList to sort the list of indexers and impose an order; added getSiteName to extract the site name from the ansible configs
• Added and fixed unit tests

[tgarg-splunk]

It is still in process. There were some error that were solved yesterday. Testing the full deployment process now

[gaurav-splunk]

Closing this since it will be covered as part of https://github.com/splunk/splunk-operator/pull/1216