Adjust IDP Docs for Zitadel to include idp-sign-key-refresh-enabled

[hadleyrich]

I have just come across an issue which took me a little while to figure out because it relys on waiting for Zitadel to rotate keys to test.

Zitadel rotates signing keys so after n hours expiry time the dashboard will no longer work as management returns 401 to api requests.

Adding --idp-sign-key-refresh-enabled to the docker-compose command config for management service solves this issue.

I would be happy to submit a PR if that's helpful but I'm not sure if it's better solved by a line in the docs or being handled automatically by the configure.sh script or whether there are plans to implement that option by default etc.

[hadleyrich]

Relates to netbirdio/netbird#808

[Fantu]

with netbirdio/netbird#1230 is possible set easier/fast in setup.env
it would be useful to add it in the doc regarding idp