This will allow us to define a set of environment variables that are
always added to the environment for pods.

Useful for things like toolforge api endpoint, etc.

Moved to a more supported lib to parse envvars, and one that allows
for adding a non-defined set of extra options. That simplifies the
helm chart values and also avoid issues with serializing maps into
strings.

Bug: T347141


Signed-off-by: David Caro <dcaro@wikimedia.org>