[Feature Request] Make Docker image customizable

[lippertmarkus]

First of all: Great work @James-Yu and @Arxisos in fully integrating my idea of #302 into this extension. This works great on every plattform.

Like another user also mentioned in #302 (comment), some may want to use a specific docker image including e.g. additional tools or a newer texlive version. Of course some could just re-tag a downloaded Docker image to tianon/latex to use it via Latex-Workshop, use the "manual way" I described in #302 or use @Arxisos shims (https://github.com/Arxisos/LaTex-Workshop-Docker) - but an option in the settings for configuring this maybe would be even more user friendly.

For the implementation I think the easiest way would be to set an environment variable before executing the scripts for *nix/Windows and using this environment variable in these scripts.

[James-Yu]

It seems possible with ${@:2} replacing $@ and $1 as the docker image in the scripts. However I currently do not have access to computers with docker. It may rely on the community effort.

[James-Yu]

Will work on this feature. Maybe the docker name can be passed through envvar.

[James-Yu]

@lippertmarkus @lukasuni if possible please have a check on this commit and see if things work as expected.

[lippertmarkus]

@James-Yu sorry for the delay - was a bit busy the last few weeks. Commit looks good to me and it also works like a charm, thank you!