Add validation for Git settings in bundles

[lennartkats-db]

Changes

This checks whether the Git settings are consistent with the actual Git state of a source directory.

(This PR adds to #577.)

Previously, we would silently let users configure their Git branch to e.g. main and deploy with that metadata even if they were actually on a different branch.

With these changes, the following config would result in an error when deployed from any other branch than main:

bundle:
name: example
workspace:
git:
branch: main
environments:
...

not on the right Git branch:
expected according to configuration: main
actual: my-feature-branch

It's not very useful to set the same branch for all environments, though. For development, it's better to just let the CLI auto-detect the right branch. Therefore, it's now possible to set the branch just for a single environment:

bundle:
name: example 2
environments:
development:
default: true
production:
# production can only be deployed from the 'main' branch
git:
branch: main

Adding to that, the mode: production option actually checks that users explicitly set the Git branch as seen above. Setting that branch helps avoid mistakes, where someone accidentally deploys to production from the wrong branch. (I could see us offering an escape hatch for that in the future.)

Testing

Manual testing to validate the experience and error messages. Automated unit tests.

[lennartkats-db]

The main thing to decide on for this PR is if we want customers to nest git under bundle... That's a lot of nesting.

This PR follows what's in main Git configuration for bundle:

bundle:
git:
branch: main

But it also adds support for setting the branch at the environment level. One way to do so could be the following:

environment:
production:
bundle:
git:
branch: main

But the nesting is pretty problematic there 😓 Instead, this PR supports:

environment:
production:
git:
branch: main

I'd still be interested in feedback on this!

[lennartkats-db]

I updated this PR so it now supports --force to override the config-specified branch.