[REQUEST]: Remote execution on different architectures

[partouf]

Before we launch an ARM instance, I would like to get ARM execution out of the way. I would like to implement this with remote execution on ARM instances. This will require a technique like #5370 tailored for the execution part, but maybe extendable to other parts.

Will require:

• Special endpoint to execute known buildpackages (for testing purposes only)
• Websockets
• Queued DB
• Mode to look in the queue (for the architecture) and execute
• Being able to make known that a certain architecture is ready for remote execution (properties? DB?)
• Making execution result available for the requesting instance
• Logging
• Live metrics

Will be making a plan to separate PR's so we don't have to get stuck with yet another long living draft.

[partouf]

#4315