ext_proc: observability mode part 4: add deferred closure timeout config

[tyxia]

The default timeout value is chosen same as drain timeout <envoy_v3_api_field_extensions.filters.network.http_connection_manager.v3.HttpConnectionManager.drain_timeout>

[repokitteh-read-only[bot]]

As a reminder, PRs marked as draft will not be automatically assigned reviewers, or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/34971 was opened by tyxia.

see: more, trace.

[repokitteh-read-only[bot]]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/). envoyproxy/api-shepherds assignee is @mattklein123 CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/34971 was opened by tyxia.

see: more, trace.

[tyxia]

/assign @yanavlasov

Edit: Yan will be OOO throughout the week, so removed the assignment.