Feature request: proper MSC3823 support in Admin API

**Description:**

Hello,

I'm working on https://github.com/etkecc/synapse-admin/pull/195 to support the MSC3823 feature in Synapse Admin, and currently (at the moment of writing using the `develop` Synapse docker tag) the following things are missing:
* Support `suspended` as one of the [List Accounts](https://element-hq.github.io/synapse/latest/admin_api/user_admin_api.html#list-accounts) params and response keys
* ~~Support `suspended` as one of the [Query User Account](https://element-hq.github.io/synapse/latest/admin_api/user_admin_api.html#query-user-account) response keys~~ Done
* Support `suspended` as one of the [Create or Modify Account](https://element-hq.github.io/synapse/latest/admin_api/user_admin_api.html#create-or-modify-account) body params

[MSC3823 is already considered stable](https://github.com/element-hq/synapse/pull/17964), but it's almost unusable in Admin API without those changes.

Thank you in advance!

PS: initially the clarifications were asked in https://github.com/element-hq/synapse/pull/17255#issuecomment-2525105226