[AIRFLOW-1629] make extra a text area so that you can actually see what you are doing

[dalupus]

Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Airflow JIRA issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-1629

Description

• Here are some details about my PR, including screenshots of any UI changes:
  The extra field in the connection is almost always used to store json. This string is often large and it is extremely difficult to work with in a text field
  Old:
  
  New:
  

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  Not sure what you would change to test this since it is visual

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[mention-bot]

@dalupus, thanks for your PR! By analyzing the history of the files in this pull request, we identified @bolkedebruin, @mistercrunch and @allisonwang to be potential reviewers.

[codecov-io]

Codecov Report

Merging #2623 into master will decrease coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2623      +/-   ##
==========================================
- Coverage   71.22%   71.14%   -0.09%     
==========================================
  Files         150      150              
  Lines       11741    11741              
==========================================
- Hits         8363     8353      -10     
- Misses       3378     3388      +10

Impacted Files	Coverage Δ
airflow/www/views.py	70.93% <100%> (ø)	⬆️
airflow/task_runner/bash_task_runner.py	93.33% <0%> (-6.67%)	⬇️
airflow/utils/helpers.py	53.44% <0%> (-2.88%)	⬇️
airflow/jobs.py	77.61% <0%> (-0.46%)	⬇️
airflow/models.py	87.15% <0%> (+0.04%)	⬆️

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[dalupus]

how did I decrease test coverage in 4 files that I didn't even touch?

[bolkedebruin]

Thanks for the contribution. Please adhere to the commit guidelines and provide a JIRA en proper commit subject/Message.

[dalupus]

@bolkedebruin is it the way you want now?