Be more defensive when managing entities in the UI if the `tenantId` is removed or invalid

## Be more defensive when managing entities in the UI if the `tenantId` is removed or invalid

### Description
On the manage entity page the `tenantId` is in the query string. If you remove it, or mangle it accidentally by copy/paste we aren't validating this parameter prior to page render. This means FreeMarker will puke and create an event log with the stack trace. 


```
==> tenantId  [in template "templates/admin/entity/manage.ftl" at line 50, column 121]
```

We could optionally kick you back to `admin/entity/` if this parameter is `null` or invalid. This would provide a better user experience. 


### Community guidelines
All issues filed in this repository must abide by the [FusionAuth community guidelines](https://fusionauth.io/community/forum/topic/1000/code-of-conduct).



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Be more defensive when managing entities in the UI if the `tenantId` is removed or invalid #1926