ci: Support nested config_path inputs

[robbowland]

What

The current config_path input option is a bit of a misnomer - it's better described as config_dir_name as providing a path that is more than a single level deep will result in the following error when reaching the west update stage:

FATAL ERROR: no west workspace found from "/__w/keymaps/keymaps"; "west update" requires one.
Things to try:
  - Change directory to somewhere inside a west workspace and retry.
  - Set ZEPHYR_BASE to a zephyr repository path in a west workspace.
  - Run "west init" to set up a workspace here.
  - Run "west init -h" for additional information.

This occurs because west init -l <dir> creates a .west folder in the parent directory of <dir> marking it as the west topdir.

In subsequent west commands, west will search up the directory tree (I think) for this .west folder.
If it doesn't find one, it'll throw the above error.

For level config_path inputs this is fine, as the parent directory is the same as the base directory the workflow is executing it. However, if we provide a multilevel path e.g. crkbd/config the command will fail as the west workspace and the base directory are no longer equivalent.

This PR fixes this by propagating the west workspace directory correctly to subsequent commands.
Example workflow.

Why

I use a nested monorepo for my keyboard configurations and want the option to use the workflow for multiple different configurations without:

• sacrificing my directory structure
• having to have a separate repo per board

This is kind of a 'power user' feature so to speak so I haven't written any docs for it.
I couldn't find any docs for non-standard workflow set-ups anyway.

[robbowland]

I suspect I may need to also change the zephyr/module.yml check to check the config parent directory.