feat: conditional stac-browser deployment

[jjfrench]

Issue

• Stac-browser should only be built on version change (security improvement) #589

What?

• Separates stac-browser deployment from veda-backend stack. Checks deployed stack tag against configured tag and deploys if values differ.

*Will need to modify veda-deploy to pull output from stac-browser-outputs.json

Why?

• Details in linked issue

Testing?

• make diff STACKS="--all"

  • shows stac-browser in its own stack
  • shows stac-browser removed from veda-backend stack
  • shows same outputs
    • Outputs
      [-] Output stacbrowserbucketname
      [-] Output stacbrowserbucketname088B771F
      [+] Output stacbrowserbucketname
      [+] Output stac-browser/bucket-name
      [+] Output StacBrowserTag StacBrowserTag

• https://github.com/NASA-IMPACT/veda-backend/actions/runs/31568417133/job/94025888621?pr=634

• Since this would be the first new deployment of the stac-browser stack, there's nothing for describe-stack to pull. Rerunning the deployment after first deployment should confirm "Tag unchanged — skipping deploy."

[jjfrench]

Once, this PR is addressed - update this to v5.0.0 to address #522
*mostly because there are three cases - stack first deploy, stack updated, stack stays the same