Enable alert group search by default (#4737)

# What this PR does

Enables free-text search on the alert group page by default (sets the
`FEATURE_ALERT_GROUP_SEARCH_ENABLED` feature flag to `True` by default).

## Which issue(s) this PR closes

Related to https://github.com/grafana/oncall/issues/4263 and
https://github.com/grafana/oncall-private/issues/2679

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## Checklist

- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
    show up in the autogenerated release notes.

engine/settings/base.py

@@ -71,7 +71,7 @@ GRAFANA_CLOUD_NOTIFICATIONS_ENABLED = getenv_boolean("GRAFANA_CLOUD_NOTIFICATION
 FEATURE_LABELS_ENABLED_FOR_ALL = getenv_boolean("FEATURE_LABELS_ENABLED_FOR_ALL", default=False)
 # Enable labels feature for organizations from the list. Use OnCall organization ID, for this flag
 FEATURE_LABELS_ENABLED_PER_ORG = getenv_list("FEATURE_LABELS_ENABLED_PER_ORG", default=list())
-FEATURE_ALERT_GROUP_SEARCH_ENABLED = getenv_boolean("FEATURE_ALERT_GROUP_SEARCH_ENABLED", default=False)
+FEATURE_ALERT_GROUP_SEARCH_ENABLED = getenv_boolean("FEATURE_ALERT_GROUP_SEARCH_ENABLED", default=True)
 FEATURE_ALERT_GROUP_SEARCH_CUTOFF_DAYS = getenv_integer("FEATURE_ALERT_GROUP_SEARCH_CUTOFF_DAYS", default=None)
 FEATURE_NOTIFICATION_BUNDLE_ENABLED = getenv_boolean("FEATURE_NOTIFICATION_BUNDLE_ENABLED", default=False)