haproxy 0.2.0 changes: Update documentation for v0.2.0 release (#931)

- Update configuration structure: replace workers with listen_tcp/listen_unix
- Remove admin_socket references
- Update log directory to /var/log/crowdsec-spoa/
- Update template paths to /var/lib/crowdsec-haproxy-spoa-bouncer/html/
- Update config file paths to /etc/crowdsec/bouncers/
- Update header names to X-Crowdsec-* (canonical form)
- Update HAProxy config examples with src-ip fallback
- Add file permission notes for crowdsec-spoa user
- Add comprehensive Configuration Reference section
- Standardize all default value mentions to (default: value) format

Author: LaurenceJJones