Fix documentation links and update IClientStore method

Updated link in documentation for HTTP 303 redirects compliance and noted required method in IClientStore.

Author: maartenba

astro/src/content/docs/identityserver/upgrades/v7_4-to-v8_0.md

@@ -239,7 +239,7 @@ dependency. Use the `CancellationToken` passed directly to interface methods ins
 ### HTTP 303 Redirects Now Unconditional
 
 IdentityServer now always uses HTTP 303 (See Other) for redirects from POST endpoints,
-in compliance with [FAPI 2.0 Section 5.3.2.2](https://openid.net/specs/fapi-2_0-security-profile.html).
+in compliance with [FAPI 2.0 Section 5.3.2.2](https://openid.net/specs/fapi-security-profile-2_0.html).
 
 ### IClientStore.GetAllClientsAsync Now Required