Feature request: Support Multi-hop for Mullvad

[hiramknick]

What's the feature 🧐

It would be great to have the ability to configure a Gluetun instance to support multihop for Mullvad.

Extra information and references

• https://mullvad.net/en/help/multihop-wireguard/
• https://mullvad.net/en/help/cli-command-wg/#multihop
• https://mullvad.net/en/blog/2022/3/10/wireguard-multihop-now-easy-available-app/
• https://github.com/jpds/mullvad-multihop

Currently the workaround is to configure 2 different concurrent Mullvad instances to house the VPN creds and make them talk to each other. With multi-hop the entire communication would be definable in a single connection.

Extra information and references

No response

[github-actions]

@qdm12 is more or less the only maintainer of this project and works on it in his free time.
Please:

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