Move Watttime credentials to .env file

[jmcook1186]

Story

As a user I want to use Watttime but don't want to expose my username and password in the manifest file.

Rationale

We should have the username and password in environment variable, similar to the Azure credentials in the azure importer plugin.

Implementation details

Remove username and password from config and instead load them from .env file.

Priority

2/5

Scope

Affects the watttime plugin

Size

0.5 d

What does "done" look like?

Watttime plugin gets credentials from environment variables

Does this require updates to documentation or other materials??

yes, update plugin readme

What testing is required?

unit tests must pass

Is this a known/expected update?

not previously discussed

[jmcook1186]

Closing as complete