fix: avoid missed logs when streaming startup logs (#8029)

* feat(coderd,agent): send startup log eof at the end

* fix(coderd): fix edge case in startup log pubsub

* fix(coderd): ensure startup logs are closed on lifecycle state change (fallback)

* fix(codersdk): fix startup log channel shared memory bug

* fix(site): remove the EOF log line

coderd/database/migrations/000127_add_startup_logs_eof.down.sql

@@ -0,0 +1 @@
+ALTER TABLE workspace_agent_startup_logs DROP COLUMN eof;

coderd/database/migrations/000127_add_startup_logs_eof.up.sql

@@ -0,0 +1,3 @@
+ALTER TABLE workspace_agent_startup_logs ADD COLUMN eof boolean NOT NULL DEFAULT false;
+
+COMMENT ON COLUMN workspace_agent_startup_logs.eof IS 'End of file reached';