feat(server): add server manager install script to support rootless docker

[Friend-LGA]

Right now default install flow is using this script

sudo bash -c "$(wget -qO- https://raw.githubusercontent.com/Jigsaw-Code/outline-server/master/src/server_manager/install_scripts/install_server.sh)"

This one doesn't work with Rootless Docker because of 2 reasons:

• --net host flag
• usage of watchtower

This PR adds new script install_server_rootless.sh which maps docker ports directly using -p flag and removes usage of watchtower.

Works with Rootless Docker (tested).

Example usage

bash -c "SHADOWBOX_DIR=$HOME/outline-data $(wget -qO- https://raw.githubusercontent.com/Jigsaw-Code/outline-server/master/src/server_manager/install_scripts/install_server_rootless.sh)"

Notice no sudo is here and custom shadowbox dir.

[google-cla]

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[fortuna]

Thanks for the contribution. However, there are a few issues:

• It doesn't fully work. If one changes the port for access keys, Docker won't be mapping those new ports, so it won't work. That's why we use --net host. We also need that to determine what ports are in use.
• It loses the history, so I can't tell what the differences are from the original script
• It introduces a lot of duplicate code to maintain

You need to address those issues in order for us to consider merging the contributions.
Why do you need Rootless mode in the first place?