fix(assets import): Ensure old datasource ids are not referenced in imported charts

[jfrag1]

SUMMARY

#23582 fixed this exact same issue, but only for the dashboard import command. I didn't realize at the time this also needed to be fixed for the assets import command (used by /api/v1/assets/import). It turns out there's a good amount of duplicated code between the different import commands, so the same fix has to be copied here as well.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

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

[michael-s-molina]

@jfrag1 Is is possible to refactor and extract said logic to a utility function or something else to avoid the copy/paste?

[jfrag1]

@jfrag1 Is is possible to refactor and extract said logic to a utility function or something else to avoid the copy/paste?

Yes it is of course possible, but due to the amount of duplication present, I think the refactor required to eliminate this duplication warrants its own PR and review process. Just check the _import methods of ImportDashboardsCommand, ImportChartsCommand, and ImportAssetsCommand to see. IMO it's ok to merge this fix PR separately since it's not really making the duplication harder to untangle (the code copied here is already duplicated between the chart and dashboard import commands).

cc @betodealmeida as I just noticed there's a relevant todo comment he left