Adds support for unix_socket

[jhgoebbert]

This PR enables RStudio connections via sockets in combination with this PR for RStudio rstudio/rstudio#14938

[jhgoebbert]

This PR also

• adds www-thread-pool-size as a possible option which can be set via the environment variable RSERVER_THREAD_POOL_SIZE
• calls rserver just once to get all supported arguments in _support_args(). This is useful as rserver might be only available through modules which takes some time to load. Therefore, this loading can be reduced.

[yuvipanda]

yay, thank you for your contribution both here and upstream to rstudio! This is going to unlock a lot of non-containerized use cases - I'm super excited for that to land :)

If you could split the PR into a unix socket one and one with everything else, that would make this easier to review and merge. I would like to hold off on merging the unix socket one until that upstream PR gets merged, but the others should be easier. Would you be open to splitting it up like that?

Thanks!

[jhgoebbert]

Thanks @yuvipanda . I will split the PR.

The PR for unix-socket support in RStudio is now merged and will be part of the official "Kousa Dogwood" builds expected in 2024.10 : rstudio/rstudio#14938 (comment)