Allow specifying a read timeout on the Pinto HTTP user agent

[fgabolde]

We have a large-ish Pinto set up, large enough that this:

pinto pull --dry-run -v Some::Module==0.123

ends up timing out after 3 minutes with

read timeout at /home/fgabolde/opt/local/pinto/lib/perl5/Net/HTTP/Methods.pm line 259.

It looks like that's the default timeout on LWP::UserAgent which Pinto::Remote::* uses behind the scenes.

Would it be possible to make this value configurable?

[thaljef]

I'll add an environment variable for it.