Add support for Account Role

[mitchnielsen]

Let's add full support for Account Roles: https://app.prefect.cloud/api/docs#tag/Account-Roles

[mitchnielsen]

I believe this is already complete. Looking at the API, there is no Create option available, so it makes sense that it's only available as a datasource right now (https://registry.terraform.io/providers/PrefectHQ/prefect/latest/docs/data-sources/account_role).

I see an Update method where you can change the name and permissions, but I don't think we actually want/need to expose that based on the comments below.

#77 (comment):

Currently, there are no plans to allow practitioners to create custom Account Roles (there is no create endpoint), and we do not allow modifying the default system roles. As such, we will just support reading down either the Admin or Member account roles by name - practitioners can then use the fetched data.prefect_account_role.foobar.id in order to set account membership in a followup resource

#39 (comment):

we no longer allow creating account roles (meaning only the default roles exist), and PATCH-ing the default roles will fail
therefore, we'll modify this issue to only scaffold the datasource, eg. reads