feat: allow configuring OIDC email claim and OIDC auth url parameters (#6867)

This commit:

- Allows configuring the OIDC claim Coder uses for email addresses (by default, this is still email)
- Allows customising the parameters sent to the upstream identity provider when requesting a token. This is still access_type=offline by default.
- Updates documentation related to the above.

site/src/api/typesGenerated.ts

@@ -516,6 +516,10 @@ export interface OIDCConfig {
   readonly scopes: string[]
   readonly ignore_email_verified: boolean
   readonly username_field: string
+  readonly email_field: string
+  // Named type "github.com/coder/coder/cli/clibase.Struct[map[string]string]" unknown, using "any"
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any -- External type
+  readonly auth_url_params: any
   readonly groups_field: string
   // Named type "github.com/coder/coder/cli/clibase.Struct[map[string]string]" unknown, using "any"
   // eslint-disable-next-line @typescript-eslint/no-explicit-any -- External type