oauth2: add "default_expires_in" config option

[riptl]

Signed-off-by: Richard Patel me@terorie.dev

Commit Message: oauth2: add "default_expires_in" config option
Additional Description: Fixes compatibility with OAuth 2.0 authorization servers that don't provide the "expires_in" property in the token response
Risk Level: Low
Testing: Added OAuth client tests for two new branches (default expires_in, missing default or explicit expires_in)
Docs Changes: Inline API proto
Release Notes: oauth2 filter: added "default_expires_in" property for authorization servers that don't provide the "expires_in" token response property
Fixes #14254
Continuation of #14625

[repokitteh-read-only]

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

🐱

Caused by: #22029 was opened by terorie.

see: more, trace.

[htuch]

Re-assigning API review to @lizan as I'm out.

[lizan]

/lgtm api

can you check CI failures?

[adisuissa]

Still waiting on CI errors fix.
/wait

[github-actions]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in 7 days if no further activity occurs. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!

[github-actions]

This pull request has been automatically closed because it has not had activity in the last 37 days. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!