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/20210915093340_UniqueHighPriorityJob.cs

@@ -0,0 +1,34 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+namespace Content.Server.Database.Migrations.Postgres
+{
+    public partial class UniqueHighPriorityJob : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateIndex(
+                name: "IX_job_one_high_priority",
+                table: "job",
+                column: "profile_id",
+                unique: true,
+                filter: "priority = 3");
+
+            migrationBuilder.CreateIndex(
+                name: "IX_job_profile_id_job_name",
+                table: "job",
+                columns: new[] { "profile_id", "job_name" },
+                unique: true);
+        }
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "IX_job_one_high_priority",
+                table: "job");
+
+            migrationBuilder.DropIndex(
+                name: "IX_job_profile_id_job_name",
+                table: "job");
+        }
+    }
+}