add 10s default timeout and environment varariable

[matuskosut]

Increases start timeout from default 5s to 15s, and allows to override using ENV variables (RSERVER_TIMEOUT, RSESSION_TIMEOUT)

• having longer timeout helps in cases when start is actually slower for any reason

Fixes #127

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[matuskosut]

hi @yuvipanda, could you review if this approach makes sense? It's pretty occasional that it takes longer than 5 seconds, but when timeout error appears it is confusing for users, because there is no action out. Having longer timeout reduces this issue significantly. Thanks.

[zeehio]

RStudio dumps workspace variables and the list of loaded packages to disk if the session is idle for a long time, and restores them when the user opens it again.

Restoring a large workspace may take a significant amount of time.

In https://docs.rstudio.com/ide/server-pro/access_and_security/running_with_a_proxy.html#check-the-connection-timeout, RStudio recommends a connect timeout of 60 seconds and a read timeout of 20 days.

Some users I worked with, when working with large workspaces (50GB), got timeout errors when restoring the Rastudio session. This is annoying because the running session becomes stuck, and they were unable to save their results after running a long task (that yielded a huge variable). I told them to change their code to avoid this, but still it would be nice to consider larger timeouts (at least 5-10 minutes) for this.

[aaraney]

@Castronova and I ran into a similar issue. This PR was able to resolve our use case.

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[ryanlovett]

Thanks @matuskosut for the PR, @aaraney and @Castronova for testing, and everyone for your patience!