Support directory and user expansion

[waketzheng]

Closes #1518

1. Support 'directory' expansion: stdout_logfile=%(directory)s/echo_time.log
2. Support 'user' expansion:

[program:api]
user=ubuntu
command=uv run --config-file /home/%(user)s/.config/uv/uv.toml app/main.py
directory=/home/%(user)s/coding/myproject
stdout_logfile=%(directory)s/logs/api.log