perf(oidc): disable push of user token meta-event (#8691)

# Which Problems Are Solved

When executing many concurrent authentication requests on a single
machine user, there were performance issues. As the same aggregate is
being searched and written to concurrently, we traced it down to a
locking issue on the used index.
We already optimized the token endpoint by creating a separate OIDC
aggregate.

At the time we decided to push a single event to the user aggregate, for
the user audit log. See [technical advisory
10010](https://zitadel.com/docs/support/advisory/a10010) for more
details.

However, a recent security fix introduced an additional search query on
the user aggregate, causing the locking issue we found.

# How the Problems Are Solved

Add a feature flag which disables pushing of the `user.token.v2.added`.
The event has no importance and was only added for informational
purposes on the user objects. The `oidc_session.access_token.added` is
the actual payload event and is pushed on the OIDC session aggregate and
can still be used for audit trail.

# Additional Changes

- Fix an event mapper type for
`SystemOIDCSingleV1SessionTerminationEventType`

# Additional Context

- Reported by support request
- https://github.com/zitadel/zitadel/pull/7822 changed the token
aggregate
- https://github.com/zitadel/zitadel/pull/8631 introduced user state
check

Load test trace graph with `user.token.v2.added` **enabled**. Query
times are steadily increasing:


![image](https://github.com/user-attachments/assets/4aa25055-8721-4e93-b695-625560979909)

Load test trace graph with `user.token.v2.added` **disabled**. Query
times constant:


![image](https://github.com/user-attachments/assets/a7657f6c-0c55-401b-8291-453da5d5caf9)

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/feature/feature.go

@@ -17,6 +17,7 @@ const (
 	KeyWebKey
 	KeyDebugOIDCParentError
 	KeyOIDCSingleV1SessionTermination
+	KeyDisableUserTokenEvent
 )
 
 //go:generate enumer -type Level -transform snake -trimprefix Level
@@ -43,6 +44,7 @@ type Features struct {
 	WebKey                          bool                      `json:"web_key,omitempty"`
 	DebugOIDCParentError            bool                      `json:"debug_oidc_parent_error,omitempty"`
 	OIDCSingleV1SessionTermination  bool                      `json:"terminate_single_v1_session,omitempty"`
+	DisableUserTokenEvent           bool                      `json:"disable_user_token_event,omitempty"`
 }
 
 type ImprovedPerformanceType int32