docs(packaging): write INSTALL-RPM.md and INSTALL-ALPINE.md

[satwareAG-ironMike]

Context

End-user documentation for installing php-firebird via YUM/dnf and apk package managers.

Acceptance Criteria

• docs/packaging/INSTALL-RPM.md exists
• Covers: adding the YUM repo, importing GPG key, installing on AlmaLinux 8/9, Fedora 41
• Shows dnf install php-firebird quickstart
• Shows verification: php -m | grep firebird
• docs/packaging/INSTALL-ALPINE.md exists
• Covers: adding the APK repo, importing RSA key, apk add php84-pecl-firebird
• Shows verification on Alpine 3.21
• Both docs document bundled FB5+ client (no firebird-dev system dep needed)
• Both docs show uninstallation

Dependencies

• Bug: Transaction::begin() uses non-autoloaded fbird_trans_begin() wrapper function #14 (YUM repo) — repo must be live
• Feature: Exception Mode API for Clean Error Handling #15 (APK repo) — repo must be live
• Feature: Stream Support for BLOB Parameters #16 (CI workflow) — automated deployment

Suggested Test Plan

1. Follow INSTALL-RPM.md on clean AlmaLinux 8 — dnf install php-firebird works
2. Follow INSTALL-RPM.md on clean Fedora 41 — works
3. Follow INSTALL-ALPINE.md on clean Alpine 3.21 — apk add php84-pecl-firebird works