Metadata import: Column selection

[ksierks]

What does this PR do and why?

Added a list of metadata columns to the file import dialog.
STRY0016737

Screenshots or screen recordings

How to set up and validate locally

Enable the new feature:

1. Launch rails console and run the following:

Flipper.enable(:metadata_import_field_selection)

2. Launch a browser and navigate to http://localhost:3000/rails/flipper/features to verify the feature has been enabled.

Test the new feature:

1. Navigate to a samples page that the logged in user has access to update.
2. Hit the Import Metadata button.
3. Select a file to import.
4. Select the Sample ID Column.
5. Select the Metadata Columns.
6. Hit the Import Metadata button.
7. Verify the sample metadata was updated.

PR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the PR acceptance checklist for this PR.

[github-actions]

Code Metrics Report

Coverage	Test Execution Time
93.2%	10m36s

Code coverage of files in pull request scope (99.0%)

Files	Coverage
app/controllers/concerns/file_import_actions.rb	100.0%
app/services/samples/metadata/file_import_service.rb	98.0%
app/views/shared/samples/metadata/file_imports/_dialog.html.erb	100.0%

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Reported by octocov