fix(dashboard): Dashboard import commands not correctly replacing charts

[lindenh]

SUMMARY

Similar to #22208, the dashboard import commands would not replace charts when the overwrite flag was true, charts would be merged into one dashboard. This change fixes the command in the exact same way as that PR.

Fixes #22127

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

1. Create a dashboard with a chart.
2. Export the dashboard for import later.
3. Modify the dashboard to remove the first chart and add a new one.
4. Import the saved dashboard earlier (via UI OR /api/v1/dashboard/import)
5. Notice both charts are in the dashboard

ADDITIONAL INFORMATION

• Has associated issue: Import dashboard/assets with overwrite flag does not replace dashboards #22127
• 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

[github-actions]

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[mdeshmu]

Please fix pre-commit by running pre-commit run --all-files

[lindenh]

Done, sorry about that!