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/feature/feature.go

@@ -9,7 +9,7 @@ import (
 type Key int
 
 const (
-	// Reserved: 3, 6
+	// Reserved: 3, 6, 8
 
 	KeyUnspecified                     Key = 0
 	KeyLoginDefaultOrg                 Key = 1
@@ -17,7 +17,6 @@ const (
 	KeyUserSchema                      Key = 4
 	KeyTokenExchange                   Key = 5
 	KeyImprovedPerformance             Key = 7
-	KeyWebKey                          Key = 8
 	KeyDebugOIDCParentError            Key = 9
 	KeyOIDCSingleV1SessionTermination  Key = 10
 	KeyDisableUserTokenEvent           Key = 11
@@ -46,7 +45,6 @@ type Features struct {
 	UserSchema                      bool                      `json:"user_schema,omitempty"`
 	TokenExchange                   bool                      `json:"token_exchange,omitempty"`
 	ImprovedPerformance             []ImprovedPerformanceType `json:"improved_performance,omitempty"`
-	WebKey                          bool                      `json:"web_key,omitempty"`
 	DebugOIDCParentError            bool                      `json:"debug_oidc_parent_error,omitempty"`
 	OIDCSingleV1SessionTermination  bool                      `json:"oidc_single_v1_session_termination,omitempty"`
 	DisableUserTokenEvent           bool                      `json:"disable_user_token_event,omitempty"`