Runtimes aren't updated when updates are pushed to the repository

[thomasgouveia]

Currently, when the registry boot up, it will download the available runtimes into /tmp/morty-runtimes.

See : https://github.com/morty-faas/morty/blob/main/registry/builder/builder.go#L68

This is an issue today, because if the registry is running and if the runtimes repository is updated during this time, we will need to restart the registry to re-download the runtimes.

The idea here is to fix this behavior by adding a mechanism to refresh the runtimes when they are updated.

One way to fix that will be to avoid downloading the runtimes on start, but download the good runtime for each build. This way, we simply ensure that all builds will use the latest version of the runtimes available. It will not impact a lot the performance of each build (depending on the network).

We can use the Subdirectories feature of the go-getter to download a specific folder from a repository.