Update JSON deserializer to handle new timestamp formats in promotions

[FE-hallen]

Changes

Please describe both what is changing and why this is important. Include:

• Endpoints added, deleted, deprecated, or changed
• Classes and methods added, deleted, deprecated, or changed
• Screenshots of new or changed UI, if applicable
• A summary of usage if this is a new feature or change to a public API (this should also be added to relevant
  documentation once released)
• Any alternative designs or approaches considered

Updated JackSonDateDeserializer to handle new promotion timestamps. Should fix errors when pulling promotions or operators.

References

Please include relevant links supporting this change such as a:

• support ticket
• community post
• StackOverflow post
• support forum thread

#19

Testing

Please describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this
library has unit and/or integration testing, tests should be added for new functionality and existing tests should
complete without errors.

• This change adds test coverage
• This change has been tested on the latest version of the platform/language or why not

I've updated existing test data to include the new promotion timestamps. Simply pulling Operators / Promotions should test if it worked or not.

Checklist

• I have read
  the Reloadly general contribution guidelines
• I have read
  the Reloadly Code of Conduct
• All existing and new tests complete without errors