On the actual runbot deployments, the `git gc` command is handled by a
unix cron. From time to time, some repositories get corrupted and we
suspect that some concurrent action may be involved as stated in
documentation [0].
For those reasons, with this commit, the `git gc` will be run by the
runbot clients themselves in order to avoid concurrent operations.
By default, the first gc will occur a few minutes after the start of the
client and the next gc are scheduled a two hours and a few minutes later.
Also, this commit ensures that the git config is written regularly in
case of change.
[0] https://git-scm.com/docs/git-gc
As for the builder, this give the ability to run the discovery of new
commits and all related logic in a separate process.
This will mainly be usefull to restart frontend without waiting for cron
or restart "leader" without stoping the frontend. This will also be
usefull for optimisation purpose.
