feat: automatically deploy new releases as PRs to sites

[mcdurdin]

When a new release is made, we should have a GHA that generates an automatic PR on each of the sites to refresh to the new release.

These PRs would still need review and merge, but this would remove the busy-work of creating each PR

[mcdurdin]

Fixed in:

• feat: trigger PR on dependent websites when release created #66
• chore: make github username global in release GHA #67
• chore: use keyman-server token for release action #68
• chore: add github token to origin in deploy-release.yml #69
• chore: fixup url for remote #70
• chore: use correct repo name in gh call #71
• chore: tweaks to release workflow #72
• chore: setup for auto-merge of release PR where supported #73

Tested in releases:

• v0.23
• v0.24
• v0.25
• v0.26
• v0.27
• v0.28
• v1.0.0
• v1.0.1

Can make further tweaks later now that the infrastructure is working (see #72, #73):

• Adding reviewers
• Labeling (to be captured by other GHA)
• Text in place (can we pull release text?)
• Link to release details as above in PR text