docs(alerts): update aggregation_delay docs for nrql alert condition

[haus]

Description

The docs appear to be wrong in how they describe aggregation_delay as there is do default delay and it is strictly required with the event_flow or cadence aggregation methods. I tried to update the wording to make that clear.

Type of change

Documentation

Checklist:

Please delete options that are not relevant.

• My commit message follows conventional commits
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation

How to test this change?

Just a docs change

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.29%. Comparing base (aea0d38) to head (04715b9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2934   +/-   ##
=======================================
  Coverage   30.29%   30.29%           
=======================================
  Files         106      106           
  Lines       29125    29125           
=======================================
  Hits         8823     8823           
  Misses      20121    20121           
  Partials      181      181           

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