[output] Adding support to add notes to incidents

[javuto]

to: @ryandeivert or @jacknagz
cc: @airbnb/streamalert-maintainers
size: small

Background

When creating incidents it may be helpful to add a note with a bit of context of what has happened or an action taken. This adds support for creating a note to a given incident.

This is just adding the functionality and the unit tests, there will be an upcoming PR to add this to the pagerduty-incidents output.

Changes

• Added ability to create a text note given an incident id.
• Added unit tests for the code.

Testing

$ rm .coverage && ./tests/scripts/unit_tests.sh
...
----------------------------------------------------------------------
Ran 533 tests in 9.331s

OK

$ ./tests/scripts/pylint.sh

--------------------------------------------------------------------
Your code has been rated at 10.00/10 (previous run: 10.00/10, +0.00)

$ python manage.py lambda test --processor rule all
...
StreamAlertCLI [INFO]: (60/60) Successful Tests
StreamAlertCLI [INFO]: (93/93) Alert Tests Passed
StreamAlertCLI [INFO]: Completed

[coveralls]

Coverage increased (+0.02%) to 95.488% when pulling 206fd8e on javier-streamalert-pagerduty-note into d508896 on master.

[jacknagz]

⭐️