MM-44953: Refactor EnsureBot to be used from plugin.API (#20521)

The mattermost-plugin-api code also needs to use this.
Hence we make it available from plugin.API.

https://mattermost.atlassian.net/browse/MM-44953

```release-note
NONE
```

plugin/api_timer_layer_generated.go

@@ -1232,3 +1232,10 @@ func (api *apiTimerLayer) GetCloudLimits() (*model.ProductLimits, error) {
 	api.recordTime(startTime, "GetCloudLimits", _returnsB == nil)
 	return _returnsA, _returnsB
 }
+
+func (api *apiTimerLayer) EnsureBotUser(bot *model.Bot) (string, error) {
+	startTime := timePkg.Now()
+	_returnsA, _returnsB := api.apiImpl.EnsureBotUser(bot)
+	api.recordTime(startTime, "EnsureBotUser", _returnsB == nil)
+	return _returnsA, _returnsB
+}