GoldenCheetah v3.8 Release Candidate 1

[Ale Martinez]

Hi, we started the release cycle for v3.8 so except for bug fixes there should be no further changes to allow for translations and documentation updated and final testing.

Highlights are:

- Joachim's work on Planned activities, enhancements to the new Calendar and new Agenda and Plan adherence charts on Plan View.

- Miguel's new user programable HTML chart for Train View

- Magnus's update to supported versions of Python

- Nathan's work to generate Apple Silicon native binaries on GitHub actions

- Felix's Tredict.com integration to sync FIT files and download Body/HRV measures and workouts

More details in https://github.com/GoldenCheetah/GoldenCheetah/releases/tag/v3.8-RC1

Thank you to all the contributors.

Enjoy, Ale.

PS: Feedback is welcome here, please don't create GitHub issues before discussion.