Fix#33966
```
;; User must sign in to view anything.
;; It could be set to "expensive" to block anonymous users accessing some pages which consume a lot of resources,
;; for example: block anonymous AI crawlers from accessing repo code pages.
;; The "expensive" mode is experimental and subject to change.
;REQUIRE_SIGNIN_VIEW = false
```
Replace #20257 (which is stale and incomplete)
Close#20255
Major changes:
* Deprecate the "WHITELIST", use "ALLOWLIST"
* Add wildcard support for EMAIL_DOMAIN_ALLOWLIST/EMAIL_DOMAIN_BLOCKLIST
* Update example config file and document
* Improve tests
