[DPE-5658] Update COS alert rules

[a-velasco]

Issue

Alert rule descriptions do not provide much guidance about what actions the user can take.

Solution

Improve the descriptions of the COS alert rule expressions where possible.

(Port of K8s changes)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.46%. Comparing base (3c7c783) to head (5fc9944).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #651      +/-   ##
==========================================
+ Coverage   71.23%   71.46%   +0.22%     
==========================================
  Files          12       12              
  Lines        3091     3073      -18     
  Branches      471      461      -10     
==========================================
- Hits         2202     2196       -6     
+ Misses        777      767      -10     
+ Partials      112      110       -2     

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[taurus-forever]

Q: why has "VALUE = {{ $value }}" been removed?

[a-velasco]

Q: why has "VALUE = {{ $value }}" been removed?

@taurus-forever This is because @7annaba3l and I were not sure whether this value reflected something meaningful. We plan to improve these expressions further and check what the values, labels, and other variables are showing.