dynamic_modules: HTTP filter config implementation

[mathetake]

Commit Message: dynamic_modules: HTTP filter config implementation
Additional Description:

This expands the ABI for HTTP filter configurations. Especially this adds two
even hooks coupled with the life cycle of HTTP filter config handled in the main
thread.

The key idea is to do the direct pointer (context) passing between the boundary;
This allows us to avoid maintaining IDs and global mapping state, which makes it
easier to test as well as it has benefit in terms of performance. E.g. there's no
need to look up "contexts" on each even hook entry.

The next follow-up PR will add per-stream event hooks (filter implementation).
After the event hooks are done, module->Envoy functions will be added (e.g.
accessing headers, etc.)

Risk Level: low
Testing: done
Docs Changes: n/a
Release Notes: n/a
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional API Considerations:]

[repokitteh-read-only]

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🐱

Caused by: #37070 was opened by mathetake.

see: more, trace.

[mathetake]

cc @marc-barry

[mathetake]

sorry for the slow progress for the last few weeks - i've been swamped by other works, now I managed to allocate some cycles on this one. The plan is after this PR, the per-stream event hooks will be implemented and then module->envoy call backs (e.g. getting headers etc) will be added. Feels like we will soon be able to provide basic functionality.

[mathetake]

/retest

[mathetake]

As a side note, Linkedin's infra team has extensively tested my PoC impl, and according to their evaluation, it's working pretty great and they observed almost zero overhead compared with the native C++ impl, which sounds awesome. The work here is and subsequent PRs will be based on their feedback as well as the original PoC implementation.