feat: create user scim v2 endpoint (#9132)

# Which Problems Are Solved
- Adds infrastructure code (basic implementation, error handling,
middlewares, ...) to implement the SCIM v2 interface
- Adds support for the user create SCIM v2 endpoint

# How the Problems Are Solved
- Adds support for the user create SCIM v2 endpoint under `POST
/scim/v2/{orgID}/Users`

# Additional Context

Part of #8140

internal/api/scim/metadata/context.go

@@ -0,0 +1,23 @@
+package metadata
+
+import (
+	"context"
+)
+
+type provisioningDomainKeyType struct{}
+
+var provisioningDomainKey provisioningDomainKeyType
+
+type ScimContextData struct {
+	ProvisioningDomain          string
+	ExternalIDScopedMetadataKey ScopedKey
+}
+
+func SetScimContextData(ctx context.Context, data ScimContextData) context.Context {
+	return context.WithValue(ctx, provisioningDomainKey, data)
+}
+
+func GetScimContextData(ctx context.Context) ScimContextData {
+	data, _ := ctx.Value(provisioningDomainKey).(ScimContextData)
+	return data
+}