chore(telco errors): update with latest known descriptions

[ajohn25]

Description

This updates the list of telco errors to account for recent changes to our understanding of certain error codes.

Motivation and Context

Combination of references to https://dev.bandwidth.com/docs/messaging/errors/ and recent responses to tickets

4750s - can be sending to prepaid AT&T numbers out of credit, but is more often a spam block when seen at high volume 4770s - blocks have been lifted when we open tickets, so we want this to be reflected 4781s - can be exceeding AT&T throughput or a spam block. Once switchboard is handling 10DLC throttling, we can update this to indicate a spam block that can be contested

How Has This Been Tested?

N/A

Screenshots (if appropriate):

Documentation Changes

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have included updates for the documentation accordingly.

[ajohn25]

@hiemanshu @lediur if i've gotten this up fast enough to make it into the release would love to merge. if not, nbd ofc