Complete release branch migration

[chillu]

• Set composer branch for master alias to on all repos (e.g. 5.x-dev or 2.x-dev)
• Alias “4.0.x-dev” to “4.x-dev” as well for people who have been installing that (it was our default branch alias on master)
• Rename all release branches to only include the major digit (e.g. 4 instead of 4.0)
• Ensure that the default branch is set to the release branch (4 or 1) for all repos
• Update open PRs that are suitable for for merge into 4.x/1.x to have 4/1 as their destination branch rather than master

---

• Make sure you can run a clean install afterwards
  • composer create-project silverstripe/installer /path/to/project 4.0.0-beta1
  • composer create-project silverstripe/installer /path/to/project 4.0.x-dev
• And Sam test this legacy alpha install with composer update

Do this for all the ~15 repos making up a core release.

• installer
• framework
• assets
• config
• versioned
• admin
• campaign-admin
• asset-admin
• siteconfig
• reports
• cms
• errorpage

excluded

• graphql

[sminnee]

We should probably alias "4.0.x-dev" to "4.x-dev" as well for people who have been installing that (it was our default branch alias on master)

To prevent this next time, I think that master's alias should be "5.x-dev" and not "5.0.x-dev"

[sminnee]

Recategorising as bug.

[sminnee]

Also you might want to add a task "Update open PRs that are suitable for for merge into 4.x/1.x to have 4/1 as their destination branch rather than master"

[flamerohr]

Can ignore the details here, it worked but I thought it didn't for a good 45 minutes!

I've been running into issues with `composer create-project silverstripe/installer /path/to/project 4.0.x-dev` which implies @sminnee's `composer update` wouldn't work, as it's producing the same error ``` The requested package silverstripe/campaign-admin 1.0.x-dev exists as silverstripe/campaign-admin[1.0.0-alpha6, 1.0.0-alpha7, 1.0.0-beta1, 1.x-dev, dev-master, 2.x-dev] but these are rejected by your constraint. ```

I had made this commit to see if branch-alias works as documented which said it needed to be on the branch.
silverstripe/silverstripe-assets@70c4eb7

This has reached the limit to my understanding with how composer works, I'll need to do some research to figure out what is happening.
Currently, I'd advise not using 1.0.x-dev/4.0.x-dev and stick with 1.x-dev/4.x-dev until this is resolved.

[sminnee]

@flamerohr you've made changes to master and they should be merged to the 4 branch.

[flamerohr]

Everything looks good, a part from mid-commit issues last night :D

Got confirmation from Sam and Damian that composer update from previous alpha installs no longer cause issues