cache: unsubscribe removed resources on reconnects

[sschepens]

When reconnections occur, envoy sends a new request subscribing to all the resources it currently had.
If a resource has just been removed, we fail to notify Envoy the the resource has been removed.

This happens because on the very first stream request, we dont have any trackedResources, we should instead also check pendingResources.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.24%. Comparing base (4577722) to head (154e449).
⚠️ Report is 94 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #320 +/- ##
============================================
+ Coverage 86.16% 86.24% +0.08% - Complexity 361 363 +2 
============================================
Files 42 42 Lines 1178 1178 Branches 97 97 ============================================
+ Hits 1015 1016 +1 + Misses 116 115 -1 
Partials 47 47 

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