Draft PR: Modify .gitmodules for CGM submodules and change default for Dexcom uploads

[marionbarker]

This is a draft PR as an example for using a different GitHub username than LoopKit for submodules to be used by Trio.

• The submodule repositories have dev or main branches aligned with LoopKit so updates can be captured as desired moving forward.
• Modifications desired for trio will go into a trio or trio_dev branch in the alternate location.
• This is a work-in-progress approach.
• The steps used for updating are subject to review and modification as directed by Trio developers.

Because the trio and trio_dev branches were aligned with LoopKit dev branch for CGMBLEKit, this PR also picks up a fix to SAGE uploads for G6 that was merged into LoopKit (PR 191). I was waiting to see if an additional pr (PR 192) would be accepted by LoopKit prior to updating Trio SHA for CGMBLEKit.

[marionbarker]

Closing to start fresh.

• request is to begin with a single PR that changes the links and branches in .gitmodules without modifying the SHA used by Trio