Add default notification text message to html

[joshuali925]

Signed-off-by: Joshua Li joshuali925@gmail.com

Description

The htmlDescription is set when user manually enters a notifications message, but it is empty with the default New report available to view and email notifications doesn't have a body.

This PR sets the default htmlDescription according to textDescription.

FYI @zhongnansu:
https://github.com/opensearch-project/notifications/blob/9a0458f590f1cb8fa98cbdefebf3ed3303669de5/notifications/spi/src/main/kotlin/org/opensearch/notifications/spi/client/EmailMimeProvider.kt#L77-L80
Although you added textPart in MimeMessage, textDescription in email channel doesn't work, only htmlDescription does. Is this expected?

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov-commenter]

Codecov Report

Merging #141 (8516c7f) into main (a238baf) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##               main     #141      +/-   ##
============================================
- Coverage     63.22%   63.21%   -0.02%     
  Complexity      297      297              
============================================
  Files            97       97              
  Lines          4128     4129       +1     
  Branches        639      639              
============================================
  Hits           2610     2610              
- Misses         1377     1378       +1     
  Partials        141      141              

Flag	Coverage Δ
dashboards-reports	73.26% <0.00%> (-0.04%)	⬇️
reports-scheduler	53.47% <ø> (ø)

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Impacted Files	Coverage Δ
...omponents/report_definitions/delivery/delivery.tsx	30.90% <0.00%> (-0.29%)	⬇️

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[zhongnansu]

I just saw your message in the PR description. Sending only text message sould work for email. I'll look into this.

[joshuali925]

closing for #184