Support getting OpenID Connect information with a function like get_idp()

**Is your feature request related to a problem? Please describe.**
I'd like to get the OpenID Connect information from ArcGIS Online or Portal. Right now I can only get SAML based Enterprise login info on ArcGIS Online using https://developers.arcgis.com/python/latest/api-reference/arcgis.gis.admin.html#arcgis.gis.admin.SecuritySettings.get_idp

```python

```

**Describe the solution you'd like**
I'd like to have the same function for OIDC, it should make the request to:
https://myorg.maps.arcgis.com/sharing/rest/portals/self/oidc?f=json
or the equivalent on Portal to get the info I need

Start with the documented SecuritySettings.get_idp function and inspect how it retrieves SAML information. Compare that behavior with the stated /sharing/rest/portals/self/oidc?f=json endpoint and its Portal equivalent. Done means exposing the corresponding OIDC information through a similarly usable function.

Written by the indexing model from the issue text.