flatpak ps: Support commit as field

Add support for commit and runtime-commit.
We shorten these to 12 characters, as we do
elsewhere.

Closes: #2027
Approved by: alexlarsson
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f