GEP: Timeouts

[youngnick]

What would you like to be added:

Gateway API needs whatever support we can do for timeouts. This GEP is to consider what timeouts are available, find some common ground, and then to implement that common ground somehow. (Very likely a Policy object, but not certain).

Why this is needed:
Timeouts are a critical part of any proxy infrastructure, and since many Gateway implementations use a proxy, they're important here as well.

[youngnick]

The first step here is a preliminary GEP PR that talks about the Why and What we need to do; in this case this includes a review of all the implementations, what dataplanes they use, and what information we have about the data plane's timeout capabilities. That should set us up for what we can do, which can then help us define what we will do.

I've already done the comparison, and am in the process of writing this PR up.

[shaneutt]

@arkodg provided several details relevant to this in #1741 which we should reference while working here.