fix: conversation duration set to 0 [CHI-3351]

[gpaoloni]

Description

This PR fixes the bug described in the ticket, where contacts' conversationDuration is always set to zero.
This bug is caused because since the contact is created in the backend, the Flex state initializes the "start timpestamp of conversation" as null.
The fix introduced here uses the contact createdAt timestamp as the start of conversation - since contacts are created in the backend, we are always guaranteed it will exist for the time the contact is loaded.

• A benefit of this approach is that conversation duration will remain even in the case of page reloads, fixing L4: Conversation duration is incorrect after refresh.
• This might imply that a small difference might exist between the time the counselor accepts the contact and what is reflected in the conversation duration: the time elapsed between the "reservation accepted" event and the time the backend actually creates the contact in HRM. Is this acceptable?
• Another implication of this change is that transferred tasks will preserve the entire time elapsed since the contact was created:
  • Counselor A accepts a chat, and keeps it open for 10 minutes.
  • Counselor A transfers the contact to Counselor B.
  • Counselor B accepts the transfer and works on it for another 20 minutes.
  • The final "conversation duration" will be computed as 30 minutes - the time elapsed since the contact creation. Is this desirable?

Checklist

• Corresponding issue has been opened
• New tests added
• Feature flags added
• Strings are localized
• Tested for chat contacts
• Tested for call contacts

Other Related Issues

None

Verification steps

AFTER YOU MERGE

1. Cut a release tag using the Github workflow. Wait for it to complete and notify in the #aselo-deploys Slack channel.
2. Comment on the ticket with the release tag version AND any additional instructions required to configure an environment to test the changes.
3. Only then move the ticket into the QA column in JIRA

You are responsible for ensuring the above steps are completed. If you move a ticket into QA without advising what version to test, the QA team will assume the latest tag has the changes. If it does not, the following confusion is on you! :-P

[stephenhand]

🚀