[ENH] Add back INCOMPLETE status handling for an imaging digest file

[alyssadai]

• Closes Bring back INCOMPLETE status in derivatives bagel #105
• See also Bring back INCOMPLETE status in derivatives bagel nipoppy/nipoppy#176

Changes proposed in this pull request:

• INCOMPLETE processing pipeline status now (re-)supported in filtering dropdowns and the digest schema
  • Pipeline status descriptions in schema updated following consultation with @nikhil153 and @michellewang
• New tooltip added to pipeline status legend in dashboard, with link to schema
• Example imaging bagel updated

Checklist

• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see https://neurobagel.org/contributing/pull_requests for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

[surchs]

looks good 🧑‍🍳