use rock in track/2.31 (#179)

* fix integration tests for OIDC in Charmed Kubeflow 1.7+ (#174)

refactors the integration test CI to:
* use the latest/edge version of oidc-gatekeeper
* provide oidc-gatekeeper with the public-url config during setup rather than during web browsing.  This is required because the oidc-gatekeeper v1.7+ will block the charm without this setting, and also because it makes more sense then changing oidc-gatekeeper settings in the fixture for a later test

Context: previously, the integration tests here incorrectly pinned OIDC to that from charmed kubeflow 1.4, which is not how we want our main branch testing to work.

* pin CI to dependencies this branch was released to

Pins the charms used by integration tests as dependencies to their stable channel at time of release of this track, not to `latest/stable` which is expected to change over time.

* use rock for dex 2.31

uses rock built from https://github.com/canonical/dex-auth-rocks/blob/track/2.31.2/dex/rockcraft.yaml

---------

Co-authored-by: Orfeas Kourkakis <orfeas.kourkakis@canonical.com>

metadata.yaml

@@ -85,4 +85,5 @@ resources:
   oci-image:
     type: oci-image
     description: OCI image for dex container
-    upstream-source: dexidp/dex:v2.31.2
+    upstream-source: charmedkubeflow/dex:2.31.2_b2b609b
+