Change wording re:unapproved txs on switch network window

**Describe the bug**
Currently the wording is confusing:
Switching networks will cancel all pending confirmations.

Some users think their existing transactions that already broadcast will be deleted or cancelled.

**Steps to reproduce (REQUIRED)**

1. Add a network from chainlist.org
2. See warning at the bottom of the window.

**Expected behavior**
Change wording to something like:
Switching networks will cancel unapproved transactions on existing network. To learn more click here. With a link to a better explanation on support.
OR
Make it conditional and just show the warning when they do have txs pending approval. And then say: Warning the existing network has transaction pending approval, if you switch networks you will lose these. Click here to view your unapproved transactions.

Also maybe state switching networks will NOT cancel transactions already submitted to the network.

Reproduce the warning by adding a network from chainlist.org and inspect the switch-network window shown in the attached screenshot. Trace the UI entry point that renders the warning; done when the wording clearly distinguishes unapproved transactions from already submitted transactions and provides the intended support or transaction link.

Written by the indexing model from the issue text.