Fix embedded-postgres PID file written before initialization

The PID file was written to the database directory before
`pg.initialise()`, which prevented initialization from succeeding.
Moved the PID file write to just after initialization but before
starting the database.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/fix-embedded-db-pid-file-timing.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli-module-build': patch
+---
+
+Fixed the embedded-postgres PID file being written before database initialization, which prevented the database from initializing successfully.