Admin API list-accounts should have a parameter to exclude appservice users

This issue has been migrated from [#11202](https://github.com/matrix-org/synapse/issues/11202).

---

**Description:**

https://matrix-org.github.io/synapse/latest/admin_api/user_admin_api.html#list-accounts

This API endpoint should have a parameter to exclude all appservice (bridged) users, ie only show native Synapse users.

And while one work on this, I suppose a flag to only show appservice users would be nice, though this is less important imo if it makes implementing this more difficult or time consuming.

This would be useful when working with servers that have a very large amount of bridged users and you need to get information about "real" users.