chore: improve build deadline code (#19203)

- Adds/improves a lot of comments to make the autostop calculation code
clearer
- Changes the behavior of the enterprise template schedule store to
match the behavior of the workspace TTL endpoint when the new TTL is
zero
- Fixes a bug in the workspace TTL endpoint where it could unset the
build deadline, even though a max_deadline was specified
- Adds a new constraint to the workspace_builds table that enforces the
deadline is non-zero and below the max_deadline if it is set
- Adds CHECK constraint enum generation to scripts/dbgen, used for
testing the above constraint
- Adds Dean and Danielle as CODEOWNERS for the autostop calculation code

coderd/database/check_constraint.go

@@ -0,0 +1,16 @@
+// Code generated by scripts/dbgen/main.go. DO NOT EDIT.
+package database
+
+// CheckConstraint represents a named check constraint on a table.
+type CheckConstraint string
+
+// CheckConstraint enums.
+const (
+	CheckOneTimePasscodeSet                        CheckConstraint = "one_time_passcode_set"                            // users
+	CheckMaxProvisionerLogsLength                  CheckConstraint = "max_provisioner_logs_length"                      // provisioner_jobs
+	CheckValidationMonotonicOrder                  CheckConstraint = "validation_monotonic_order"                       // template_version_parameters
+	CheckMaxLogsLength                             CheckConstraint = "max_logs_length"                                  // workspace_agents
+	CheckSubsystemsNotNone                         CheckConstraint = "subsystems_not_none"                              // workspace_agents
+	CheckWorkspaceBuildsAiTaskSidebarAppIDRequired CheckConstraint = "workspace_builds_ai_task_sidebar_app_id_required" // workspace_builds
+	CheckWorkspaceBuildsDeadlineBelowMaxDeadline   CheckConstraint = "workspace_builds_deadline_below_max_deadline"     // workspace_builds
+)