Add Out of Date Agents as a warning in overview of UI

#### Feature Description

Per [this doc](https://developer.hashicorp.com/consul/docs/upgrading#large-version-jumps) consul servers are recommended to be no further than two revisions ahead of agents.

The ask is to have a list of agents who are two or more revisions behind the current server version in the UI overview.

#### Use Case(s)

As an administrator this solves a huge management issue for others in the same position.

Start with the linked Consul upgrade documentation and the UI overview named in the issue. Determine how the overview exposes server and agent versions, then define the warning for agents two or more revisions behind. Done means those out-of-date agents are listed in the overview with a clear warning.

Written by the indexing model from the issue text.