Document PHP-FPM max_children warning

[altis-assistant]

Describe the PR

Adds a note to the dashboard logs documentation for the common PHP-FPM warning:

server reached pm.max_children setting, consider raising it

The note clarifies that this warning is expected on Altis Cloud and is generally not relevant/actionable because request capacity is handled through horizontal autoscaling of web containers rather than increasing PHP-FPM workers within a single container.

Related support context: Zendesk #11334.

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For Altis Team Use

Completion Checklist

Does this PR meet our definition of done? See the Play Book Definition of Done

• Has the acceptance criteria been met?
• Is the documentation updated (including README)?
• Do any code/documentation changes meet project standards?
• Are automatic tests in place to verify the fix or new functionality?
  • OR, are manual tests documented (at least on the ticket/PR)?
• Are any Playbook/Handbook pages updated?
• Has a new module release (patch/minor) been created/scheduled?
• Have the appropriate backport labels been added to the PR?
• Is there a roll-out (and roll-back) plan, if required?