file-restore: add binary and basic commands

For now it only supports 'list' and 'extract' commands for 'pxar.didx'
files. This should be the foundation for a general file-restore
interface that is shared with block-level snapshots.

This is packaged as a seperate .deb file, since for block level restore
it will need to depend on pve-qemu-kvm, which we want to seperate from
proxmox-backup-client.

[original code for proxmox-file-restore.rs]
Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

[code cleanups/clippy, use helpers::list_dir_content/ArchiveEntry, no
/block subdir for .fidx files, seperate binary and package]
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

debian/rules

@@ -52,8 +52,11 @@ override_dh_dwz:
 
 override_dh_strip:
 	dh_strip
-	for exe in $$(find debian/proxmox-backup-client/usr \
-	  debian/proxmox-backup-server/usr -executable -type f); do \
+	for exe in $$(find \
+	    debian/proxmox-backup-client/usr \
+	    debian/proxmox-backup-server/usr \
+	    debian/proxmox-file-restore/usr \
+	    -executable -type f); do \
 	  debian/scripts/elf-strip-unused-dependencies.sh "$$exe" || true; \
 	done