relax start/end date formats

[alexnikitchuk]

What

fix for #360

How

Use default click.DateTime formats %Y-%m-%d, %Y-%m-%dT%H:%M:%S, %Y-%m-%d %H:%M:%S

[stevenayers]

@mateuszklimek This feature would be useful - I'm running my notification every 15 minutes. Any chance we could get it merged?

[davidzajac1]

@alexnikitchuk @stevenayers sorry for the hold up on this one. I ran our setup_toy_shop.sh shell script we use to test changes but I changed one of the commands to use %Y-%m-%d %H:%M:%S format and got the following error:

Error: Invalid value for '--start-date': '2021-01-07 11:00:00' does not match the format '%Y-%m-%d'

Looks like there is probably some other datetime related changes needed in the command_line.py file. Also I updated our CONTRIBUTING.md to make it easier for anyone to run these tests locally.