Add workaround for automatically testing the repo

[jongpie]

Salesforce does not currently allow the metadata deploy method to be executed in a unit test - that makes this repo nearly impossible to properly test using Apex tests. As a possible workaround,

1. Create an 'extra tests' folder that is only used by the pipeline (similar to Apex-Rollups)
2. Include a flow in that folder that uses the invocable methods - this will serve as the 'test'
3. In the repo's pipeline, deploy all metadata to a scratch org (including the extra folder)
4. Run an apex script to execute the flow, and check the deployment ID for any errors. If any errors occur, fail the build.

[jamessimone]

It ain't pretty, but it sure doth work