[redcap] repeated field ordering and configuration

[regisoc]

Brief summary of changes

This PR adds a new configuration for the repeated instrument index field choice.
Imported repeated records will be ordered automatically based on the chosen field.

• Have you updated related documentation?

Testing instructions (if applicable)

1. test with a repeated instrument set up

[MaximeBICMTL]

I really like the idea of using redcap_repeat_instance to get the index of a repeated instrument record (that's basically what I had in mind when I wrote the TODO comment). Do we still also need the timestamp-based approach though? If we only have the former we can always know the index of a repeated record independently of other records, which is a lot cleaner IMO (and allows us to get rid of the RedcapRecord inheritance hierarchy eventually)

[ridz1208]

@regisoc has this been updated according to the latest discussion ?

[regisoc]

@ridz1208 not yet in sync.
@MaximeBICMTL I still want to have the timestamp option, as we discover new way of handling REDCap data. The problem on the timestamp is because of user error. In a project, some users are entering data as admin which is skipping the init of multiple fields... and in any case, I made redcap_repeat_instance as the default.