Allow PCUI to support multiple Pcluster versions

[hgreebe]

Description

Allow PCUI to support managing clusters of different PCUI versions

Changes

• PCUI template accepts a comma separated list of versions to support
• An API stack for each pcluster version is launched
• API handler manages the mapping of pcluster version to api invoke url
• Each API request contains a version parameter in the url
• Updating the stack to remove or add support for different pcluster versions is supported
• During cluster create the first page is now a version page that includes a dropdown menu to select a version
• The official Images page includes a dropdown menu to select which version of images to show

How Has This Been Tested?

• Manually Tested the following:
  • Create PCUI stack with the version parameter filled in with multiple versions
  • Validated that you could see info and modify clusters of the multiple supported versions
  • Validated creating clusters of multiple versions
  • Validated updating clusters of multiple versions
  • Validated view the official images of different versions
  • Validated that buttons such as Shell DCV and Stop Fleet work for only the supported versions
  • Validated that clusters of unsupported versions are not editable
  • VAlidated updating the stack by removing and adding supported versions
• Modified unit tests to account for support of multiple versions

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