Ensure /sbin/tini exists

[NickDickinsonWilde]

When using mysql image in lando, it fails hard (but unfortunately mostly silently)
lando logs:

mariadb_1  | lando 05:09:06.08 INFO  ==> Lando handing off to: /sbin/tini -- /lagoon/entrypoints.bash mysqld
mariadb_1  | /lando-entrypoint.sh: line 86: /sbin/tini: No such file or directory

which causes the mysqld server to never start.

This appears to be caused because some shared files expect tini in /sbin/ but in this image it is by default at /usr/bin/

[tobybellwood]

Nice pickup @NickDickinsonWilde - no idea why I did this one differently to all the other non-alpine ones - we try to avoid copying the alpine binary into the non-alpine images - so we use krallin/tini instead

I've created a branch with a co-authored commit with the fix the way we do it in other images - happy for you to update your PR to match if you want full credit, or I can close this and merge the co-authored one?

main...testing/mysql_tini

[NickDickinsonWilde]

co-authored is totally fine for sure. Definitely makes sense to not copy the binary - I had also considered doing the same thing I did to locally fix (ln -s /usr/bin/tini /sbin/tini) but found examples of copying that binary in other images. Example: https://github.com/uselagoon/lagoon-images/blob/main/images/nginx/Dockerfile (I don't know if any instances of that want changing as well?)... oh that's alpine to alpine so fine.