Reset FTL config values to default if they are not set in environment variables?

[PromoFaux]

If you start the container with, for example, FTLCONF_debug_all: 'true', and then stop the container and remove that environment variable - debug.all will still be enabled in FTL.

As it stands, if you want to turn it off again you have to explicitly set FTLCONF_debug_all: 'false', which is far from ideal.

Perhaps we should add in some code that sets the FTL config to default on every container start, and applies any FTLCONF environment variables onto that.

This would mean though that any customisations made to this file in a volume mounted directory would be overwritten on every restart. Perhaps this is OK.