governance: updating review changes (envoyproxy#30995)

Risk Level: n/a
Testing: n/a
Docs Changes: yes
Release Notes: no

Signed-off-by: Alyssa Wilk <[email protected]>

CONTRIBUTING.md

@@ -237,18 +237,19 @@ Please note that if adding a runtime guarded feature, your [release notes](chang
 * Typically we try to turn around reviews within one business day.
 * See [OWNERS.md](OWNERS.md) for the current list of maintainers.
 * It is generally expected that a senior maintainer should review every PR to
-  core code. Test-only or extension-only changes need only be reviewed by a
-  maintainer, or senior extension maintainer.
+  core code. Changes which only touch tests, extensions, tools, docs or comments
+  need only be reviewed by a maintainer, or senior extension maintainer.
 * It is also generally expected that a "domain expert" for the code the PR touches should review the
   PR. This person does not necessarily need to have commit access.
-* The previous two points generally mean that every PR should have two approvals. (Exceptions can
-  be made by the senior maintainers).
-* The above rules may be waived for PRs which only update docs or comments, or trivial changes to
-  tests and tools (where trivial is decided by the maintainer in question).
-* In general, we should also attempt to make sure that at least one of the approvals is *from an
+* For new extensions (contrib or otherwise) and features, at least one of the approvals should be *from an
   organization different from the PR author.* E.g., if Lyft authors a PR, at least one approver
   should be from an organization other than Lyft. This helps us make sure that we aren't putting
   organization specific shortcuts into the code.
+  new HTTP/3 features are largely exempt from cross-company approvals as all of the
+  area experts work at a single company, but HTTP/3 changes which impact general
+  functionality still merit a cross-company check.
+* contrib extensions do not need senior maintainer or maintainer review only contrib owner review and
+  a maintainer stamp to merge.
 * If there is a question on who should review a PR please discuss in Slack.
 * Anyone is welcome to review any PR that they want, whether they are a maintainer or not.
 * Please make sure that the PR title, commit message, and description are updated if the PR changes