Improve first-time experience for people setting up escalation policies

Problem

From #337237 (closed) - when someone is setting up an escalation policy for the first time, the following things could be helpful:

• Some indication in the empty state of how people will be notified (email, text?)
• Help text for the name field
• Introduce a success message when a policy has been set up, re-assuring them that the process is complete, along with what will happen now that they have a policy created

Proposal

We can address these problems with three small changes:

1. Updated empty state text

Update the single line description text in the empty state, as outlined here:

2. Updated help text

Introduce help text under the name and description fields, as outlined here:

3. Success message

Introduce a success message when the escalation policy has been successfully added:

Figma file