Retry message sending logic for Secure Conversations

[EgorovEI]

MOB-3597

What was solved?
This commit:

• adds retry logic for Secure Conversations transcript screen;
• adds units tests

Snapshot test will be added in next PR

Release notes:

• Feature
• Ignore
• Release notes (Is it clear from the description here?)
• Migration guide (If changes are needed for integrator already using the SDK - what needs to be communicated? Add underneath please)

Additional info:

• Is the feature sufficiently tested? All tests fixed? Necessary unit, acceptance, snapshots added? Check that at least new public classes & methods are covered with unit tests
• Did you add logging beneficial for troubleshooting of customer issues?
• Did you add new logging? We would like the logging between platforms to be similar. Refer to Logging from iOS SDKs → Things to consider for newly added logs in Confluence for more information.

[igorkravchenko]

Looks good to me 👍