Proper dependency caching in the CI, and Docker Hub cache registry

[Litarvan]

Description

• Dependencies will now be cached in the Docker CI
• Docker Hub is now used instead of GitHub as cache registry, since it has no space limit

Type of change

Please select the right one.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Which part is impacted ?

• Daemon
• Wallet
• Miner
• Misc (documentation, comments, text...)

Checklist

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

[Slixe]

lgtm