Continue after folders migration errors

[bonclay7]

What does this PR do?

🛑 Please open an issue first to discuss any significant work and flesh out details/direction - we would hate for your time to be wasted. Consult the CONTRIBUTING guide for submitting pull-requests.

Motivation

Currently, when we run the migrator twice or if folders already exist, the migration will stop. This keep in memory the source reference and allows migration to continue and attempt dashboards migration

A bit of https://github.com/aws-observability/amazon-managed-grafana-migrator/issues/21

More

• [x] Yes, I ran pre-commit run -a with this PR
• [x] Yes, I added unit tests for new code added (as much as possible)

Note: Not all the PRs require unit tests

Additional Notes

[bonclay7]

Creating temporary API key for g-a4
Creating temporary API key for g-c1

Migrating data sources:
Data source: Prometheus ws-c32b1e35-2c70-430b-ba88-015ca441f399
    warning: status: 409, body: {"message":"data source with the same name already exists","traceID":""}
✔ Migrated 0 data sources

Migrating folders:
Folder: Folders-Test
Folder: Prom-3
    error: Prom-3 [status: 412, body: {"message":"the folder has been changed by someone else","status":"version-mismatch"}]
Folder: Prometheus
    error: Prometheus [status: 412, body: {"message":"the folder has been changed by someone else","status":"version-mismatch"}]
Folder: Test-UID
    error: Test-UID [status: 412, body: {"message":"the folder has been changed by someone else","status":"version-mismatch"}]
✔ Migrated 1 folders

Migrating dashboards:
Dashboard: /d/WBVPPq34z/prom
    warning: status: 412, body: {"message":"The dashboard has been changed by someone else","status":"version-mismatch"}
✔ Migrated 0 dashboards

Skipping alert rules migration

Removing temporary API key for g-c1

Removing temporary API key for g-a4