Prep v6 beta release

[nicolethoen]

Tasks

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1. Make sure all extensions are up to date with all changes on main branches
2. Identify beta release candidate
3. Add featured Medium article for the PatternFly 6 beta. #4116
   Content +1
   
4. Add beta release highlights #4137
   Content +1
   
5. Update all extensions to use beta release
6. Add extension docs to v6 once they're updated with betas #4168
   +0
   
7. Ensure codemods are complete
8. Update testing template and let testers/products know beta candidates
9. set up v5-archive.patternfly.org #3991
   P1 ⭐ +1
   

Now, post beta release, but immediately after:

Tasks

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1. Rename branches (v6 -> main, main -> v5)
2. Update configs in all repos to stop releasing alphas and begin releasing prereleases
3. Update configs in v5 branches to continue releasing v5