Rename notify whole Slack channel (#4577)

# What this PR does
rename "Notify whole Slack channel" escalation step into "Escalate to
all slack channel members"

## Which issue(s) this PR closes

Closes https://github.com/grafana/oncall/issues/4373

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## Checklist

- [ ] 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.

docs/sources/configure/escalation-chains-and-routes/index.md

@@ -83,7 +83,7 @@ from an on-call schedule.
 * `Notify all users from a team` - send a notification to all users in a team.
 * `Resolve incident automatically` - resolve the alert group right now with status
 `Resolved automatically`.
-* `Notify whole slack channel` - send a notification to the users in the slack channel. These users will be notified
+* `Escalate to all Slack channel members` - send a notification to the users in the slack channel. These users will be notified
 via the method configured in their user profile.
 * `Notify Slack User Group` - send a notification to each member of a slack user group. These users will be notified
 via the method configured in their user profile.
@@ -97,7 +97,7 @@ Useful when you want to get escalation only during working hours
 passes some threshold
 * `Repeat escalation from beginning (5 times max)` - loop the escalation chain
 
-> **Note:** Both "**Notify whole Slack channel**" and "**Notify Slack User Group**" will filter OnCall registered users
+> **Note:** Both "**Escalate to all Slack channel members**" and "**Notify Slack User Group**" will filter OnCall registered users
 matching the users in the Slack channel or Slack User Group with their profiles linked to their Slack accounts (ie. users
 should have linked their Slack and OnCall users). In both cases, the filtered users satisfying the criteria above are
 notified following their respective notification policies. However, to avoid **spamming** the Slack channel/thread,

docs/sources/manage/notify/slack/index.md

@@ -135,7 +135,7 @@ and users:
 Once your Slack integration is configured you can configure Escalation Chains to notify via Slack messages for alerts
 in Grafana OnCall.
 
-There are two Slack notification options that you can configure into escalation chains, notify whole Slack channel and
+There are two Slack notification options that you can configure into escalation chains, escalate to all Slack channel members and
 notify Slack user group:
 
 1. In Grafana OnCall, navigate to the **Escalation Chains** tab then select an existing escalation chain or

engine/apps/alerts/models/escalation_policy.py

@@ -128,7 +128,10 @@ class EscalationPolicy(OrderedModel):
         ),
         STEP_FINAL_RESOLVE: ("Resolve alert group automatically", "Resolve alert group automatically"),
         # Slack
-        STEP_FINAL_NOTIFYALL: ("Notify whole Slack channel", "Notify whole Slack channel"),
+        STEP_FINAL_NOTIFYALL: (
+            "Escalate to all Slack channel members (use with caution)",
+            "Escalate to all Slack channel members (use with caution)",
+        ),
         STEP_NOTIFY_GROUP: (
             "Start {{importance}} notification for everyone from Slack User Group {{slack_user_group}}",
             "Notify Slack User Group",