Made members JWKS endpoint caching configurable

refs https://github.com/TryGhost/Toolbox/issues/411
refs f58b5984cb

- Having hardcoded cache control values in the codebase makes it impossible to experiment with new values without a version release.
- Having all values configurable by default will allow for easier caching experiments and customizations on self-hosting instances.
- This change only changes the members endpoint caching configurability. The other JWKS endpoint will be modified separately (following commit), to keep changes concise

ghost/core/core/frontend/web/site.js

@@ -94,7 +94,7 @@ module.exports = function setupSiteApp(routerConfig) {
     // /member/.well-known/* serves files (e.g. jwks.json) so it needs to be mounted before the prettyUrl mw to avoid trailing slashes
     siteApp.use(
         '/members/.well-known',
-        shared.middleware.cacheControl('public', {maxAge: constants.ONE_DAY_S}),
+        shared.middleware.cacheControl('public', {maxAge: config.get('caching:wellKnown:maxAge')}),
         (req, res, next) => membersService.api.middleware.wellKnown(req, res, next)
     );
 

ghost/core/core/shared/config/defaults.json

@@ -126,6 +126,9 @@
         "robotstxt": {
             "maxAge": 3600000
         },
+        "wellKnown": {
+            "maxAge": 86400
+        },
         "cors": {
             "maxAge": 86400
         }