[FEATURE REQUEST] environment file serializer

[nicholasmhughes]

Describe the solution you'd like
A common workflow is to create environment files, which have an = between a key and value. It would be nice to have a serializer to handle that formatting.

Describe alternatives you've considered
file.keyvalue can perform a similar purpose, but it can't completely overwrite the file without invoking another state... and there also may be some value in having the functionality in a serializer for other non-state invocations.

Additional context
Format:

FOO=bar

Please Note
If this feature request would be considered a substantial change or addition, this should go through a SEP process here https://github.com/saltstack/salt-enhancement-proposals, instead of a feature request.

[OrangeDog]

Would it be better described as a properties file, or simply a keyvalue file?

The serializer should be named for the structure/format, not for one particular use for it.