feat: Update docs for slow burn alerts

[akane0915]

Description

The documentation for NRQL alert conditions should be updated to reflect the updated allowed maximum for aggregation_window and the corresponding slide-by changes.

Fixes (issue)

Type of change

Please delete options that are not relevant.

• This change requires a documentation update

Checklist:

Please delete options that are not relevant.

• My commit message follows conventional commits
• My code is formatted to Go standards
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• New and existing unit tests pass locally with my changes. Go here for instructions on running tests locally.

How to test this change?

Ensure updated documentation makes sense and reflects the goals described in the ticket.

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #2476 (9a45f35) into main (947f861) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2476   +/-   ##
=======================================
  Coverage   33.82%   33.82%           
=======================================
  Files          91       91           
  Lines       24918    24918           
=======================================
  Hits         8429     8429           
  Misses      16333    16333           
  Partials      156      156           

Files	Coverage Δ
newrelic/resource_newrelic_nrql_alert_condition.go	30.66% <ø> (ø)

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[akane0915]

@mbazhlekova Please do not merge this PR yet. It is not ready. I'll let you know when it's ready. Thank you!

[akane0915]

@mbazhlekova This is ready to be merged and released now. Thank you!