OAuth: Support OIDC Hybrid Flow

**What would you like to be added**: Support for the OIDC Hybrid Flow. See [Auth0](https://auth0.com/docs/api-auth/tutorials/hybrid-flow), [Medium](https://medium.com/identity-beyond-borders/openid-connect-hybrid-flow-1123bc9461fe), [Scott Brady](https://www.scottbrady91.com/OpenID-Connect/OpenID-Connect-Flows) **Why is this needed**: Some Identity Providers do not support Authorization Code flow or require PKCE for the Authorization Code flow. Hybrid Flow adds an additional layer of security on top of the normal Authorization Code flow without requiring PKCE and while still using a client secret. Specifically, [OSIsoft Cloud Services](https://cloud.osisoft.com/), my company's flagship cloud service, offers authorization only by Client Credentials, Authorization Code + PKCE, and Hybrid flow. Since the only compatible method with Grafana is Client Credentials, it is not feasible to have individual users log in, instead our customers must use an organization-wide client secret stored within the Grafana server. Hybrid flow is preferred over Auth+PKCE because, in our system, Auth+PKCE is not allowed to issue a refresh token while Hybrid is, and Grafana needs a refresh token to keep users logged in and leave dashboards open over long periods. I created #26302 for this feature and it was rejected on the grounds that there is no community support for this; if you are interested in this feature please comment or thumbs-up.