Refine connector provider registry per review

Three follow-ups from review of the registry consolidation:

- Build Vercel's authorization URL with net/url instead of a
  hand-rolled "{integration_slug}" placeholder resolved by
  strings.ReplaceAll. The slug is escaped via url.PathEscape in a
  per-provider Registration.BuildAuthURL closure, and the unused
  AuthURLParams plumbing on Registration and OAuth2Connector is
  removed (OAuth2Connector now carries a typed IntegrationSlug).

- Drop the SettingsInput union type and the per-provider
  MarshalSettings closures. The create resolvers now build the typed
  coredata.*ConnectorSettings directly from the gqlgen input, the
  same way the OAuth callback path already does, so there is no
  shared catch-all DTO and no stringly-typed boundary.

- Restore ConnectorProviders() to a plain ordered slice literal; the
  intermediate map + slices.Sort added nondeterminism and a sort for
  no benefit.

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

pkg/connector/provider/github.go

@@ -16,7 +16,6 @@ package provider
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"net/http"
 
@@ -37,13 +36,6 @@ func githubRegistration() *Registration {
 		ExtraSettings: []ExtraSetting{
 			{Key: "organization", Label: "Organization", Required: true},
 		},
-		MarshalSettings: func(in *SettingsInput) (json.RawMessage, error) {
-			if in == nil || in.GitHubOrganization == nil || *in.GitHubOrganization == "" {
-				return nil, fmt.Errorf("cannot create github connector: githubOrganization is required")
-			}
-
-			return json.Marshal(&coredata.GitHubConnectorSettings{Organization: *in.GitHubOrganization})
-		},
 		NewDriver: func(_ context.Context, c *http.Client, conn *coredata.Connector, logger *log.Logger) (drivers.Driver, error) {
 			s, err := coredata.ConnectorSettings[coredata.GitHubConnectorSettings](conn)
 			if err != nil {