change some default settings inline with what the golang default http

[MFAshby]

...client settings are

hoping to avoid some odd behaviour around idle connections

[leonyork]

I've not looked into if these are sensible numbers for the new transport settings you're using (apart from the testing you've done elsewhere), but/so I think it's worth making them configurable and setting the current values as the defaults.

[leonyork]

Can we make these configurable as command line arguments (like the others), so that we can tune this without releasing a new version of regproxy?

[MFAshby]

I copied and pasted these from the default configuration and possible I shouldn't have...

Both are irrelevant for our use case (test-control doesn't use TLS, nor does it use HTTP 100-continue responses.)

I could make them configurable for the convenience of others who might be using these features but it won't help us.

[leonyork]

Thanks for explaining. Approved.