fix: Unable to export multiple Dashboards with the same name

[diegomedina248]

SUMMARY

Users can export multiple Dashboards in a single ZIP.
However, selecting two Dashboards with the same name won’t work properly - only one is included on the export file.

This PR follows the same approach taken for the charts, and adds the dashboard id at the end of the file name.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Example:

TESTING INSTRUCTIONS

1. Navigate to Dashboards.
2. Click on + DASHBOARD.
3. Name your dashboard - for example, Export Test.
4. Click on SAVE.
5. Navigate back to Dashboards.
6. Click on + DASHBOARD.
7. Use the same title for this Dashboard.
8. Click on SAVE.
9. Navigate back to Dashboards.
10. Click on BULK SELECT.
11. Select both Dashboards.
12. Click on EXPORT.

Ensure two files are created under dashboards folder.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• 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

Merging #20383 (e2f00ca) into master (86f146e) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head e2f00ca differs from pull request most recent head c01877c. Consider uploading reports for the commit c01877c to get more accurate results

@@            Coverage Diff             @@
##           master   #20383      +/-   ##
==========================================
- Coverage   66.52%   66.52%   -0.01%     
==========================================
  Files        1739     1739              
  Lines       65141    65141              
  Branches     6900     6900              
==========================================
- Hits        43336    43335       -1     
- Misses      20052    20053       +1     
  Partials     1753     1753              

Flag	Coverage Δ
mysql	82.29% <100.00%> (ø)
postgres	82.36% <100.00%> (ø)
python	82.44% <100.00%> (-0.01%)	⬇️
sqlite	82.09% <100.00%> (ø)
unit	?

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

Impacted Files	Coverage Δ
superset/dashboards/commands/export.py	83.78% <100.00%> (ø)
superset/initialization/__init__.py	91.13% <0.00%> (-0.36%)	⬇️

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[rusackas]

Eagle eyes! :)

[rusackas]

LGTM. I'd merge it, but I would love a stamp from @betodealmeida or @eschutho to make sure there aren't some other implications (perhaps on the import side of the equation) that I'm unaware of.

[eschutho]

LGTM! Thanks @diegomedina248