docs: prometheus-setup alert table lists 10 of the 14 chart alerts

[SebTardif]

docs/guides/prometheus-setup.md says the Helm PrometheusRule creates 10 alerts. The chart ships 14.

The table in that guide omits these alerts from charts/attune/templates/prometheusrule.yaml:

• AttunePodsInfeasible
• AttunePodsDeferred
• AttuneGitOpsPRFailures
• AttuneMemoryLimitUnsafe

Copy the "when it fires" text from each alert's expr and annotations, and the default severity and for duration from charts/attune/values.yaml under metrics.prometheusRule.rules. Do not invent thresholds.

No new test is needed. charts/attune/tests/prometheusrule_test.yaml already asserts that the chart renders 14 alerts. This change is the guide table only. Do not add a parser that checks the markdown table.

This issue is reserved for a first-time contributor. Please leave the ready label off.

Done when

• The opening sentence count matches the number of - alert: entries in the chart template.
• Every chart alert has one table row: name, when it fires, default severity.
• The table does not name an alert the chart does not ship.

Pull request

Use a title like docs: list every prometheusrule alert in the setup guide. The subject after docs: must start with a lowercase letter. Commit with git commit -s.