Update branches RFC #1025

[vpetrovykh]

Set up instance-specific and project-specific way to specify the current branch. Both of them de facto exist, but they were not coordinated resulting in bugs.

[vpetrovykh]

We have 2 ways of specifying branches:

1. As part of the instance credentials
2. As part of project configuration

Our branch CLI tools all work with the instance credentials to keep track of the current branch. However, linking a cloud instance to a project allows to override the branch associated with the cloud instance via a different mechanism. In addition to the instance config we have a project config that allows to override instance-name, cloud_profile, project-path, and database. This mechanism predates our branches concept.

The database setting was introduced by edgedb/edgedb-cli#1086 in order to allow multiple projects to be linked to the same cloud instance, but using different databases.

Unfortunately this way of setting the current branch is buggy in our CLI tools. Which leads to a situation where CLI branch tools work fine for local instances, but adding and the removing a cloud instance may cause database to be overridden. The CLI tools then read this database setting as the current branch, but they don't update it when switching branches, so the branch is stuck.

[vpetrovykh]

There is no reason why projects with local and cloud instances should treat branches differently. So we need to make them use the settings consistently.

It seem that we have 2 scenarios:

1. branch commands targetting an instance

   If a branch command has an explcit -I option, it should refer to and modify the instance credentials (ignoring project database setting).

2. project branch commands

   If a branch command omits -I and relies on the project settings, it must never modify the instance credentials, instead updating the branch (or database when already present) in the project settings (regardless of whether this is a local or cloud instance).

[aljazerzen]

Great, we are on the same page.