Review "Setup automation for dex via dex-operator" documentation

[gawertm]

The documentation to set up automation for Dex via Dex operator may need to be reviewed and possibly extended.

Recently we received a few support cases when GS engineers encountered issues with SSO configuration when setting up a new installation. For example:

• It is not always clear how to create a config for Dex operator using an existing one from a different installations
• One step of the authentication setup requires admin approval and it is not always clear what to do in that case

More context: https://gigantic.slack.com/archives/C053JHJC99Q/p1692953495490229

[stone-z]

I have looked at this but I think I'll need help from the expert. @ssyno can you see if anything needs to be updated in this doc? Maybe include a link to your existing ops recipes for dex if any of the content is the same, rather than duplicating it here