Add extra unique constraints to DB jobs.

1. Can only have one high-priority job now. This actually got messed up for at least 10 people in the production DB and I fixed them manually.
2. Can't have duplicate jobs with the same name on the same profile.

Content.Server.Database/Migrations/Postgres/PostgresServerDbContextModelSnapshot.cs

@@ -196,6 +196,13 @@ namespace Content.Server.Database.Migrations.Postgres
 
                     b.HasIndex("ProfileId");
 
+                    b.HasIndex("ProfileId", "JobName")
+                        .IsUnique();
+
+                    b.HasIndex(new[] { "ProfileId" }, "IX_job_one_high_priority")
+                        .IsUnique()
+                        .HasFilter("priority = 3");
+
                     b.ToTable("job");
                 });