Add a hot reloading RIE side implementation

[dfangl]

Motivation

We want to provide hot reloading to be able to mount a volume into the container and see changes as they happen. For this, once a change happens, we have to reset the infrastructure, to support reloading (for example, a loaded python module will not change if the source changes, we have to reload it / restart the interpreter).

Changes

• Add recursive filewatcher for the /var/task folder, to be alerted if something changes
• Add a debounced function to reload 500ms after last file change (to prevent too many restarts due to massive file changes)

Todos

• Check functionality on windows and mac, and add polling mode if necessary
• Add separate env variables to watch /var/task and /opt respectively? Or a even better, a list of to-be-watched directories.

[dominikschubert]

Looking forward to this feature! 😁

Added a few nits and suggestions.

Especially the main logic block in RunFileWatcher would benefit a lot from deconstructing it into smaller functions and introducing a struct for the filewatcher.

A few other suggestions for now:

• separate the debounce from the actual consumption/processing of the changes for more clarity (e.g. the debounce itself could be a wrapper around the channel)
• prefer passing a context instead of a channel for signaling exit/done

[dominikschubert]

small nit/suggestion, otherwise LGTM