add hidden prop to connector config

[johnvan7]

Overview

Added config property to hide a connector in the login web page, for example if it should be used only for m2m.

What this PR does / why we need it

As requested in #3145 and #4231

Adds connector's config property "hidden" (default false).

Related

Discussion: Can I hide a connector? #3145

[cardoe]

@nabokihms and @sagikazarmark what do you think of this?

[cardoe]

To further this along, I've pulled this PR into build that I made at https://github.com/cardoe/dex/releases/tag/v2.44.90 You can grab the container to test with at ghcr.io/cardoe/dex:v2.44.90 and report back on this PR.

[johnvan7]

Hi @cardoe, I've tested ghcr.io/cardoe/dex:v2.44.90 with the connector property "hidden: true" and it works as expected!