Rename unstable to main throughout codebase

[shonfeder]

Closes #1012

NOTE: This PR is into the new branch named main, which will be made the default once this PR is is approved by the team.

Overview

The trunk of our development has been called unstable for a long time.
This is a holdover from before we adopted a trunk-based development
model, and from before we had CI/CD running for the trunk. Now, the
trunk is really not very unstable, and stability is given by versioned
releases, rather than by maintaining long-lived branches in parallel.

After this change, we should be able to reconfigure the default branch.

Notable changes

• Renamed all mention of the unstable branch to main
• Updated docs on installing from docker

Reviewing

With the exception of the update to the docker installation instructions and the changelog entry (both isolated in their own commits), the change effected here was purely mechanical, with the exception of the changelog entry. It couldn't hurt to have some sanity checks that I've not missed anything or altered anything I shouldn't have.

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• Entries added to ./unreleased/ for any new functionality

[codecov-commenter]

Codecov Report

Merging #1990 (dbf13fd) into main (a86dcb7) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head dbf13fd differs from pull request most recent head a5a479a. Consider uploading reports for the commit a5a479a to get more accurate results

@@            Coverage Diff             @@
##             main    #1990      +/-   ##
==========================================
- Coverage   77.83%   77.82%   -0.02%     
==========================================
  Files         418      418              
  Lines       12813    12789      -24     
  Branches      584      566      -18     
==========================================
- Hits         9973     9953      -20     
+ Misses       2840     2836       -4     

Impacted Files	Coverage Δ
...in/scala/at/forsyte/apalache/tla/lir/Feature.scala	0.00% <ø> (ø)
...n/scala/at/forsyte/apalache/tla/lir/TlaType1.scala	83.14% <ø> (-0.02%)	⬇️
...rsyte/apalache/tla/typecheck/TypeCheckerTool.scala	92.30% <0.00%> (-0.38%)	⬇️
.../forsyte/apalache/io/typecheck/parser/tokens.scala	92.85% <0.00%> (-0.25%)	⬇️
...syte/apalache/io/typecheck/parser/Type1Lexer.scala	95.55% <0.00%> (-0.10%)	⬇️
...ache/tla/typecheck/etc/TypeAliasSubstitution.scala
...apalache/tla/typecheck/etc/ConstSubstitution.scala	58.97% <0.00%> (ø)
...lache/io/typecheck/parser/DefaultType1Parser.scala	95.45% <0.00%> (+0.55%)	⬆️
...he/io/annotations/parser/CommentPreprocessor.scala	97.80% <0.00%> (+1.09%)	⬆️
... and 1 more

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[shonfeder]

This is cleanup from long ago :)

[Kukovec]

Question, what happens to all the PRs in flight? Does GH know to change "XYZ wants to merge N commits into unstable from branch" or do they break?

[konnov]

Good idea! I don't see any major issues with that, except that we would have to manually retarget active pull requests against trunk.

[thpani]

I support moving away from unstable, but isn't trunk a very Subversion-y name?
Both Git and GitHub use main as the default branch name.

[thpani]

We also already use main on the Cloud and TNT repos.

[shonfeder]

Question, what happens to all the PRs in flight? Does GH know to change "XYZ wants to merge N commits into unstable from branch" or do they break?

We’ll have to change the branch they are targeting the pending prs.

[shonfeder]

We also already use main on the Cloud and TNT repos.

Ah good point. When the change away from master was happing, I configured my git config to use trunk, and I prefer it cause it fits with the branching metaphor, but forgot that it is less common. I’ll change this to main.

[shonfeder]

Changed this to target main and to switch out the development branch name to main.

[thpani]

👍