Enable automatic refresh of signing keys for Google IDP (#246)

References: netbirdio/netbird#2269

Author: jgoclawski

src/pages/selfhosted/identity-providers.mdx

@@ -997,6 +997,7 @@ NETBIRD_TOKEN_SOURCE="idToken"
 NETBIRD_AUTH_DEVICE_AUTH_PROVIDER="none"
 
 NETBIRD_MGMT_IDP="google"
+NETBIRD_MGMT_IDP_SIGNKEY_REFRESH=true
 NETBIRD_IDP_MGMT_EXTRA_SERVICE_ACCOUNT_KEY="<BASE64_SERVICE_ACCOUNT_KEY>"
 NETBIRD_IDP_MGMT_EXTRA_CUSTOMER_ID="<GOOGLE_WORKSPACE_CUSTOMER_ID>"
 ```