Auth Proxy: replace ini setting ldap_sync_ttl with sync_ttl (#20191)

* Renamed ttl config in code to be more consistent with behaviour
* Introduced new setting `sync_ttl` in .ini file
* Keeping the old setting `ldap_sync_ttl` in the .ini file as fallback and compatibility.

pkg/middleware/auth_proxy/auth_proxy.go

@@ -92,7 +92,7 @@ func New(options *Options) *AuthProxy {
 		headerType:          setting.AuthProxyHeaderProperty,
 		headers:             setting.AuthProxyHeaders,
 		whitelistIP:         setting.AuthProxyWhitelist,
-		cacheTTL:            setting.AuthProxyLDAPSyncTtl,
+		cacheTTL:            setting.AuthProxySyncTtl,
 		LDAPAllowSignup:     setting.LDAPAllowSignup,
 		AuthProxyAutoSignUp: setting.AuthProxyAutoSignUp,
 	}