POC: Add environment variable injection to plugin

[ryanolee]

What?

This a proof of concept for the proposal given in #76

Why?

To show the viability of implementing such a change.

How?

Currently this PR parses the new configuration option and adds environment variables to the handler associated with the file. There is no duplication detection / function specific isolation but this should be possible by copying the handlers js file and later on updating the handler config to use the file with the isolated ENV over the shared handler file.

What needs doing still:

In the event this is seen to be a reasonable feature to implement proper environment separation / collection will need to be set up. Beyond that documentation will need to be written preferably with a set of unit tests. If possible support should also be added for python runtimes using the os.environ over the process.env variable.

Beyond that a few tests need writing for the implementation.

In theory we could use something like https://webpack.js.org/plugins/environment-plugin/ over injecting the env vars ourselves 🤔

[coveralls]

Coverage decreased (-3.1%) to 13.187% when pulling 7b046e8 on ryanolee:feature/InjectEnv into 157f0af on silvermine:master.

[coveralls]

Coverage decreased (-3.1%) to 13.187% when pulling 7b046e8 on ryanolee:feature/InjectEnv into 157f0af on silvermine:master.