fix(accounts): fix the account domains payload

[mitchnielsen]

Summary

Fixes the payload type of account domains.

The API docs don't show the structure of the response, so we mistakenly assumed it was the same as the request payload - a list of strings.

It's actually a list of objects, and the name is one of the fields in those objects.

So this change accounts for that structure, and extracts the names from it.

Follow-up to #382

Closes #390

Testing

You can't create accounts with Terraform, and to test SSO it has to be enabled on a paid account, so I used the existing github-ci-tests account we have in staging:

terraform {
  required_providers {
    prefect = {
      source = "registry.terraform.io/prefecthq/prefect"
    }
  }
}

provider "prefect" {
  endpoint = "https://api.stg.prefect.dev"
  account_id = "bb19c492-73c2-4ecd-9cd7-d82c4aac08e6"
  api_key = "<redacted>"
}

resource "prefect_account" "test" {
  name   = "github-ci-tests"
  handle = "github-ci-tests"
  # Added "update.com"
  domain_names = ["example.com", "foobar.com", "update.com"]
  settings = {
    ai_log_summaries        = true
    allow_public_workspaces = false
    managed_execution       = true
  }
}

Per the comment, I added update.com to my Terraform (the first two existed already because I manually set them to satisfy the datasource acceptance test).

I applied the change and it added the value as expected:

Terraform will perform the following actions:

  # prefect_account.test will be updated in-place
  ~ resource "prefect_account" "test" {
      ~ domain_names = [
            # (1 unchanged element hidden)
            "foobar.com",
          + "update.com",
        ]
        id           = "bb19c492-73c2-4ecd-9cd7-d82c4aac08e6"
        name         = "github-ci-tests"
      ~ updated      = "2025-02-28T22:41:58Z" -> (known after apply)
        # (3 unchanged attributes hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes

prefect_account.test: Modifying... [id=bb19c492-73c2-4ecd-9cd7-d82c4aac08e6]
prefect_account.test: Modifications complete after 1s [id=bb19c492-73c2-4ecd-9cd7-d82c4aac08e6]

Apply complete! Resources: 0 added, 1 changed, 0 destroyed.

This covers the resource testing. The datasource testing, as mentioned, is part of the acceptance test suite as of this PR.

Requirements

General

• The contributing guide has been read
• Title follows the conventional commits format
• Body includes Closes <issue>, if available
• Relevant labels have been added
• Draft status is used until ready for review

Code-level changes

• Unit tests are added/updated
• Acceptance tests are added/updated (including import tests, when needed)

New or updated resource/datasource

• Documentation is added (generated by make docs from source code)
  - When applicable, provide a link back to the relevant page in the Prefect documentation site.
• For resources, the following are added:
  - Resource example under examples/resources/prefect_<name>/resource.tf
  - Import example under examples/resources/prefect_<name>/import.sh
• For datasources, the following is added:
  - Datasource example under examples/data-sources,resources>/prefect_<name>/data-source.tf