contrib: add a lua module allowing to display cdba board status with conky

[brgl]

Conky is a light-weight system monitor that can be easily customized with lua scripts.

I'm running my cdba lab with a small display using conky to display system information. I wrote this lua script that uses the information about the cdba lock files and the cdba config to determine which boards are being used and for how long.

It can be easily integrated into conky.conf like so:

$hr
${color grey}cdba:$color
${lua cdba 1 status}
${lua cdba 2 status}
${lua cdba 3 status}
${lua cdba 4 status}

I figured it may be useful to others and it makes sense to carry it in the cdba repo.

[lumag]

THanks!