west: Update fish completion for `boards`

With the recent change to hwmv2, loading the
boards is extremely slow and can take several
seconds.

To solve that problem this commit add a cache
of the boards. The cache is updated based on:
    - when the latest commit of the manifest
    file directory is updated or;
    - when the manifest file directory is not
    a git directory, when the manifest file
    content itself is updated.

At the same time:
    - update how the board completion is
    displayed by including the board vendor to it;
    - add missing `--board` and `--board-dir`
    options;
    - remove `hwmv1` board completion code.

Signed-off-by: Théo Battrel <theo.util@protonmail.ch>