feat: SMTP as a fallback function when Sendgrid quota exceeds limit

[mrsaicharan1]

Fixes #5958

Checklist

• I have read the Contribution & Best practices Guide and my PR follows them.
• My branch is up-to-date with the Upstream development branch.
• The unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

• All the functions created/modified in this PR contain relevant docstrings.

Short description of what this resolves:

• creates a centralized task rather than having two separate tasks for them
• Checks for Sendgrid quota value and decides the protocol

Changes proposed in this pull request:

• Added centralised task send_email_via_smtp
• Add check for SMTP fallback

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (development@47363b9). Click here to learn what that means.
The diff coverage is 7.54%.

@@              Coverage Diff              @@
##             development   #5981   +/-   ##
=============================================
  Coverage               ?   66.1%           
=============================================
  Files                  ?     285           
  Lines                  ?   14122           
  Branches               ?       0           
=============================================
  Hits                   ?    9335           
  Misses                 ?    4787           
  Partials               ?       0

Impacted Files	Coverage Δ
app/api/helpers/mail.py	29.29% <7.14%> (ø)
app/api/helpers/tasks.py	17.58% <8%> (ø)

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[iamareebjamal]

@mrsaicharan1

Tests are failing because your code is trying to send emails and failing:

 File "/home/travis/build/fossasia/open-event-server/app/api/auth.py", line 225, in reset_password_post
    send_email_with_action(user, PASSWORD_RESET, app_name=get_settings()['app_name'], link=link)
  File "/home/travis/build/fossasia/open-event-server/app/api/helpers/mail.py", line 119, in send_email_with_action
    html=MAILS[action]['message'].format(**kwargs)
  File "/home/travis/build/fossasia/open-event-server/app/api/helpers/mail.py", line 87, in send_email
    send_email_task_sendgrid.delay(payload=payload, headers=headers)
...
File "/home/travis/build/fossasia/open-event-server/app/api/helpers/tasks.py", line 76, in send_email_task_sendgrid
    sendgrid_client.send(message)
  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/sendgrid/sendgrid.py", line 98, in send
    response = self.client.mail.send.post(request_body=message.get())
  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/python_http_client/client.py", line 252, in http_request
    return Response(self._make_request(opener, request, timeout=timeout))
  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/python_http_client/client.py", line 176, in _make_request
    raise exc
python_http_client.exceptions.UnauthorizedError: HTTP Error 401: Unauthorized

[iamareebjamal]

Found the freaking culprit: https://api.eventyay.com/#settings-settings-details-patch

Not only it sets the sendgrid key to a random value, it also changes the environment to production!!!

Fix the docs and the error will be gone. Just change the app-environment to testing

[iamareebjamal]

Something else is changing the app config. Need to debug more

[mrsaicharan1]

@iamareebjamal This is only due to the random app config change right? Because I made sure that the email is not being sent when neither of them are configured.

[iamareebjamal]

Yes, it is due to config changes

[mrsaicharan1]

@iamareebjamal Looks good I guess. Travis seems to go through now :)

[mrsaicharan1]

@iamareebjamal Please have a look now.