Add OKTA connector provider enum and settings

Introduce the OKTA value to the connector_provider enum (Go const,
ConnectorProviders slice, IsValid switch, GraphQL @goEnum, and the
Postgres ALTER TYPE migration) and an OktaConnectorSettings struct
holding the customer's Okta org domain.

Okta is a per-tenant IdP with no central API gateway, so the
connector is keyed on the org domain rather than a shared host. The
oktaDomain field on CreateAPIKeyConnectorInput lets the API-key flow
carry it.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/coredata/connector_provider.go

@@ -58,6 +58,7 @@ const (
 	ConnectorProviderAnthropic    ConnectorProvider = "ANTHROPIC"
 	ConnectorProviderCursor       ConnectorProvider = "CURSOR"
 	ConnectorProviderDatadog      ConnectorProvider = "DATADOG"
+	ConnectorProviderOkta         ConnectorProvider = "OKTA"
 )
 
 var (
@@ -103,6 +104,7 @@ func ConnectorProviders() []ConnectorProvider {
 		ConnectorProviderAnthropic,
 		ConnectorProviderCursor,
 		ConnectorProviderDatadog,
+		ConnectorProviderOkta,
 	}
 }
 
@@ -143,7 +145,8 @@ func (v ConnectorProvider) IsValid() bool {
 		ConnectorProviderTailscale,
 		ConnectorProviderAnthropic,
 		ConnectorProviderCursor,
-		ConnectorProviderDatadog:
+		ConnectorProviderDatadog,
+		ConnectorProviderOkta:
 		return true
 	}