feat: BW-3310 add dateformat to the email subject

[US579]

SUMMARY

Problem
If the subject remains the same, all scheduled reports will be delivered in the same email thread, requiring the recipient to scroll back to the original thread to find the latest email.

However, if a date is included in the email subject, the emails will not be grouped in the same thread. To address this, I propose adding a feature that allows users to specify a date format in the email subject, enabling the email client to correctly thread the emails and display them in a more organized manner.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before

After

TESTING INSTRUCTIONS

set DATE_FORMAT_IN_EMAIL_SUBJECT=True

and add date format in the email subject

available date format

https://strftime.org/

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags: DATE_FORMAT_IN_EMAIL_SUBJECT (by default is disabled)
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 83.74%. Comparing base (76d897e) to head (60378db).
Report is 1170 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/reports/notifications/email.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #31413       +/-   ##
===========================================
+ Coverage   60.48%   83.74%   +23.25%     
===========================================
  Files        1931      537     -1394     
  Lines       76236    39069    -37167     
  Branches     8568        0     -8568     
===========================================
- Hits        46114    32717    -13397     
+ Misses      28017     6352    -21665     
+ Partials     2105        0     -2105     

Flag	Coverage Δ
hive	48.75% <63.63%> (-0.42%)	⬇️
javascript	?
mysql	76.44% <81.81%> (?)
postgres	76.53% <81.81%> (?)
presto	53.26% <63.63%> (-0.54%)	⬇️
python	83.74% <90.90%> (+20.25%)	⬆️
sqlite	75.99% <81.81%> (?)
unit	60.88% <81.81%> (+3.25%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.