SAML Support for docker

[LoveSkylark]

Added a new variable that allows the docker to install plugins that are needed for SAML.

"rebased"

[dot-mike]

I have one issue with this... INSTALL_PLUGINS is set-up so installing plugins only happens after container is started because it's a service in root-fs. That means running lnms plugin:add will require internet to work. Not everyone has internet access after an image is built and will be running internally ;)

A better way would be to install the plugins in Dockerfile during image build, all though this requires more steps to ensure things are done in the right order.

[LoveSkylark]

This is by design - installing third-party plugins in the Docker image has two major drawbacks:

1. You'd need to maintain and regularly update all included plugins within the image
2. You'd need to predict and include all possible plugins users might need

Note: If you don't have Internet access, you likely won't be using SAML auth anyway.

This approach is a compromise - plugins are installed during container startup if needed, rather than being pre-installed. While this adds some startup time, it keeps the image lean and flexible, allowing you to use plugins only when required. The installation only occurs when the "INSTALL_PLUGINS" variable is set, so it only affects those willing to accept that startup cost.