Add additional fields for pending channels

[sairina]

Description

When dealing with invitations, the model for Channels had not been updated to include revoked, declined, and accepted, as per the new Invitation models. This PR updates that in the pending_channels

Checklist

Delete any items that don't apply

• Is the code clean and well-commented?
• Are views organized into pages, components, and layouts directories as described in the docs?

[codecov]

Codecov Report

Merging #2994 (3ef91ae) into hotfixes (28587f8) will increase coverage by 4.94%.
The diff coverage is 92.92%.

@@ Coverage Diff @@## hotfixes #2994 +/- ##
============================================
+ Coverage 80.80% 85.74% +4.94% 
============================================
Files 281 298 +17 Lines 12659 15845 +3186 ============================================
+ Hits 10229 13587 +3358 + Misses 2430 2258 -172 

Impacted Files	Coverage Δ
contentcuration/contentcuration/decorators.py	56.60% <50.00%> (-37.60%)	⬇️
...ntentcuration/contentcuration/db/models/manager.py	91.20% <90.98%> (-8.80%)	⬇️
contentcuration/contentcuration/forms.py	82.35% <94.04%> (+33.89%)	⬆️
contentcuration/contentcuration/api.py	92.06% <100.00%> (+1.43%)	⬆️
...tentcuration/contentcuration/context_processors.py	100.00% <100.00%> (ø)
...ontentcuration/contentcuration/db/advisory_lock.py	100.00% <100.00%> (ø)
...tcuration/contentcuration/db/models/expressions.py	93.33% <100.00%> (-6.67%)	⬇️
...entcuration/contentcuration/db/models/functions.py	100.00% <100.00%> (ø)
...ation/contentcuration/tests/test_rest_framework.py	36.93% <0.00%> (-63.07%)	⬇️
contentcuration/contentcuration/utils/format.py	21.05% <0.00%> (-49.54%)	⬇️
... and 181 more

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[rtibbles]

Follow up from #2529