Add a namespace to all used environment variables

[alexppg]

Is your feature request related to a problem? Please describe.
There's some environmental variables that pyms uses, like CONFIGMAP_FILE or KEY_FILE. Those are very generic names, if you see them without context, you might don't know why are they set and what are they purpose.

Describe the solution you'd like
I propose to add a namespace to all variables, so KEY_FILE would be PYMS_KEY_FILE.

Describe alternatives you've considered
None.

Additional context
None.

If you guys agree, I might do this change myself.

[avara1986]

It`s a good idea 👍

In retrospective, the last refactor of the configuration, we did some bad actions. We changed all schema and not announce it.

I propose add this change but preserve the old way and show a warning of deprecation in futures versions, what do you think?

[alexppg]

I agree. They should be removed at some time, but it doesn't have to break it at the next release.
Also, a changelog should be generated on every release, with a special section with "breaking changes".

[rapejim]

I think I could try to make this issue.

[alexppg]

Nice, thanks @rapejim !