feat: add custom Caddy modules to the static binary

[dunglas]

Add custom Caddy modules to static binaries.

Example with Souin, Mercure and Vulcain:

XCADDY_ARGS="--with github.com/darkweak/souin/plugins/caddy --with github.com/dunglas/mercure/caddy --with github.com/dunglas/vulcain/caddy"  \
./build-static.sh

Closes #1208, closes #982, closes #591.

TODO:

• docs

[dunglas]

The error in the CI is super weird

[vittodevit]

Tried testing the branch locally but the error is exactly the same.
It seems to crash at one of the last steps of the static-build.sh file when it's defining the environment variables?

[withinboredom]

How big is the environment + command? It looks like what you used to get when your total command length + env exceeded the maximum back in the day.

[vittodevit]

Ok, i found the time to do a couple more tests.
Without using the container, i ran directly the build-static.sh file and this is where it crashes: https://dpaste.com/6NVEGLWN2
The env i used is this: https://dpaste.com/HTVXLJM84
Running it without the env gives the exact same error.

[dunglas]

This seems to work now, but I'm not sure why...