Xero refresh token not retained

[jhogendorn]

The tap-xero does not properly store the refresh token, so when it runs each time the token is invalidated and you have to have a human do the init auth flow again.

https://meltano.slack.com/archives/C01TCRBBJD7/p1691310724043439

Suggested fix is to alter the tap to use bookmarks. examples:

Read: https://github.com/s7clarke10/pipelinewise-tap-mssql/blob/f7a0bf18c01d24aa55ce5fbc8b3bc7ee9c928fc7/tap_mssql/sync_strategies/log_based.py#L289
Write: https://github.com/s7clarke10/pipelinewise-tap-mssql/blob/f7a0bf18c01d24aa55ce5fbc8b3bc7ee9c928fc7/tap_mssql/sync_strategies/log_based.py#L389C93-L389C93

If it can track whatever the last refresh token it was given is this will work.

Relevant lines in tap-xero:

Read: https://github.com/singer-io/tap-xero/blob/16dd78c8ee6c77245d45876fc0f6d9e4a41a387d/tap_xero/client.py#L198
Write: https://github.com/singer-io/tap-xero/blob/16dd78c8ee6c77245d45876fc0f6d9e4a41a387d/tap_xero/client.py#L208