DM-42994: Improve messages for LTD Keeper-related errors (for 0.8.3 release)

[jonathansick]

Provide a good error message and ensure that the readable text always appears at the bottom of the log.

• For failures to register the build, differentiate between cases where the project itself doesn't exist from cases when a simultaneous build is being uploaded. The message tell the user to either re-try later, or contact support in the case of the project not existing.
• For failures to confirm the build, have the user always contact dm-docs-support.