Make proxy.config.http2.accept_no_activity_timeout and proxy.config.http2.no_activity_timeout_in overridable/reloadable

[mlibbey]

These 2 http configs are overridable:

proxy.config.http.transaction_no_activity_timeout_in
proxy.config.http.transaction_no_activity_timeout_out

but, the corresponding http2 configs

proxy.config.http2.accept_no_activity_timeout and 
proxy.config.http2.no_activity_timeout_in 

are not. Seems like we should be consistent. (or, do we really need these as separate configs? it's a bit annoying to think to keep them in sync.

[zwoop]

@mlibbey Can you prioritize / assign this please ?