Add rsyncable gzip

[ThomDietrich]

Hello,
thanks for this image! It is probably a fairly typical use case to leverage your image to create a backup of a database, which in turn will be stored on some backup server. As backup solutions, like restic, implement deduplication features it actually makes a huge difference to use the --rsyncable option with gzip. Sadly I had to find out that your image carries an old gzip version. Would you please consider adding a newer version? Thanks!

Please see:

• https://beeznest.wordpress.com/2005/02/03/rsyncable-gzip/
• Documentation: Best practice wrt pre-compressed data restic/restic#2886