Update KiCad.gitignore

[krishnans2006]

Reasons for making this change:
When using KiCad with git/GitHub, I always use a modified version of the official KiCad.gitignore file with these changes applied. New KiCad versions have changed the way backups and autosaves are performed, and this PR hopes to reflect those changes in this repository.

Enumerated list of changes:

1. Add *-cache*
2. Generalize *.sch-bak to *-bak and *-bak*
3. Add ~*
4. Add #auto_saved_files#

Links to documentation supporting these rule changes:

• 1, 2, 4: TechOverflow notes the KiCad-generated gitignore. Changes 1, 2, and 4 make this repo's file more consistent with the KiCad recommendation.
• 3: Reddit notes the introduction of lock files in KiCad v8.

Another Credit: #4176 (comment) for one of this PR's changes.