chore(oidc): graduate webkey to stable (#10122)

# Which Problems Are Solved

Stabilize the usage of webkeys.

# How the Problems Are Solved

- Remove all legacy signing key code from the OIDC API
- Remove the webkey feature flag from proto
- Remove the webkey feature flag from console
- Cleanup documentation

# Additional Changes

- Resolved some canonical header linter errors in OIDC
- Use the constant for `projections.lock` in the saml package.

# Additional Context

- Closes #10029
- After #10105
- After #10061

internal/api/saml/certificate.go

@@ -14,13 +14,14 @@ import (
 	"github.com/zitadel/zitadel/internal/crypto"
 	"github.com/zitadel/zitadel/internal/eventstore"
 	"github.com/zitadel/zitadel/internal/query"
+	"github.com/zitadel/zitadel/internal/query/projection"
 	"github.com/zitadel/zitadel/internal/repository/instance"
 	"github.com/zitadel/zitadel/internal/repository/keypair"
 	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
 const (
-	locksTable = "projections.locks"
+	locksTable = projection.LocksTable
 	signingKey = "signing_key"
 	samlUser   = "SAML"