oidcConfig.rootCA does not apply to sessionManager oidc provider

**Describe the bug**

The oidcConfig.rootCA should apply to all usages of the OIDC provider. However, this config is not used by the sessionmanager.go created provider which is causing x509 errors.

**To Reproduce**

Login through dex with an OIDC provider using a self-signed certificate. The initial redirect to dex did not work until the rootCA config was added. Then everything seemed to go fine until the redirect back to argocd.

**Expected behavior**

The oidcConfig.rootCA should apply to all usages of the OIDC provider.

**Screenshots**

**Version**
v2.3.1+b65c169

**Logs**

```
time="2022-05-25T00:53:06Z" level=info msg="Initializing OIDC provider (issuer: https://dexe03777d4.eks.local)"
time="2022-05-25T00:53:21Z" level=info msg="finished unary call with code Unauthenticated" error="rpc error: code = Unauthenticated desc = invalid session: Failed to query provider \"https://dex.e03777d4.eks.local\": Get \"https://dex.e03777d4.eks.local/.well-known/openid-configuration\": x509: certificate signed by unknown authority" grpc.code=Unauthenticated grpc.method=List grpc.service=application.ApplicationService grpc.start_time="2022-05-25T00:53:06Z" grpc.time_ms=15013.107 span.kind=server system=grpc
```

Work around appears to be mapping an extra volume per [this](https://github.com/argoproj/argo-cd/issues/4344#issuecomment-890382825)