Fix templates for safe rendering of comments, pipeline & property descriptions

[kiersten-stokes]

Fixes #2461
This also fixes a recent bug (no corresponding issue currently open) where certain Airflow operators were causing an error popup with JsonDecodeError due to unescaped characters in property descriptions.

What changes were proposed in this pull request?

• Converts pipeline descriptions and node comments (in the airflow DAG template) to multi-line strings (""") using the jinja replace filter and escapes any other existing instances of """ to avoid black formatting errors after DAG render.

DAG:

Airflow GUI:

• Converts property descriptions (in the canvas properties template) to JSON-safe strings using jinja's tojson|safe filter. This allows un-escaped characters to be caught before descriptions are converted to JSON in the properties API request.

Python operator file (source):

Properties panel:

How was this pull request tested?

A case has been added to an existing test for each scenario above.

This PR will remain in draft form until more manual testing occurs.

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[ptitzler]

The following comment cannot be handled by the proposed solution. This comment

line feeds
line feeds
can you handle """
yes you can!

yields

Cannot parse: 59:0: op_b12bffe0_8734_4719_bed5_a4e11668f50e.image_pull_policy = 'IfNotPresent'

[ptitzler]

LGTM

[lresende]

Could you make the title string to fit the commit title guidelines