Make sure all in-use env vars are represented in env.sample

[MikeTheCanuck]

There are at least two "new" environment variables in play this year, that might or might not be relevant to local development usage:
#51 (comment) (comment entitled "New env vars in play this year").

There may be others that weren't captured, that are documented in this comment:
#51 (comment)

[znmeb]

Can we close this? I think we have all the environment variables documented.

[nam20485]

Closing. All existing variables to-date are represented and comment added for description in the sample.env