Move workspace.db API field to database_name

The fact that this attribute lives on `workspace` is an internal Job
Server implementation detail that we don't want to expose in the API it
presents to Job Runner (specifically because we want to change it
shortly).

The corresponding PR in Job Runner, which must be deployed first, is:
 * https://github.com/opensafely-core/job-runner/pull/6509

jobserver/api/jobs.py

@@ -229,7 +229,6 @@ class Meta:
             "name",
             "repo",
             "branch",
-            "db",
             "created_by",
             "created_at",
         ]
@@ -257,6 +256,7 @@ class Meta:
                 "created_by",
                 "created_at",
                 "workspace",
+                "database_name",
                 "project",
                 "orgs",
             ]

jobserver/models/core.py

@@ -365,6 +365,13 @@ def status(self):
 
         return "unknown"
 
+    @property
+    def database_name(self):
+        # TODO: This is temporary code. We're going to remove the `workspace.db` column
+        # entirely and use different logic for decided which database a job runs
+        # against.
+        return self.workspace.db
+
 
 class Org(models.Model):
     """An Organisation using the platform"""

tests/unit/jobserver/api/test_jobs.py

@@ -808,11 +808,11 @@ def dictify(od):
             "project": project.slug,
             "requested_actions": ["frob", "wizzle"],
             "sha": "",
+            "database_name": "full",
             "workspace": {
                 "name": workspace.name,
                 "repo": workspace.repo.url,
                 "branch": "",
-                "db": "full",
                 "created_by": workspace.created_by.username,
                 "created_at": now_iso,
             },
@@ -828,11 +828,11 @@ def dictify(od):
             "project": project.slug,
             "requested_actions": ["frobnicate", "wibble"],
             "sha": "",
+            "database_name": "full",
             "workspace": {
                 "name": workspace.name,
                 "repo": workspace.repo.url,
                 "branch": "",
-                "db": "full",
                 "created_by": workspace.created_by.username,
                 "created_at": now_iso,
             },
@@ -848,11 +848,11 @@ def dictify(od):
             "project": project.slug,
             "requested_actions": ["analyse"],
             "sha": "",
+            "database_name": "full",
             "workspace": {
                 "name": workspace.name,
                 "repo": workspace.repo.url,
                 "branch": "",
-                "db": "full",
                 "created_by": workspace.created_by.username,
                 "created_at": now_iso,
             },