MedEvac: per-dataset Common Services user filter

[morgang-adappt]

Description

Adds a per-dataset Common Services user filter for separate-email datasets, so recipients can be selected from the Common Services user directory instead of, or alongside, a per-row email field. Filter values may be {{Block N.field}} tokens taken from the dataset itself, which the function resolves per row at send time. This introduces a dataset-token editor in the filter row and forwards the available field settings to it, and stabilises the expression editor's token options with a memoised field list and trackBy, fixing value choices that were unclickable on production builds.

Also adds the general-flow toggle that lets a separate-email dataset be sent to the distribution list as well as its own recipients, and loosens the distribution list requirement to match.

Useful links

• Please insert link to ticket
• MedEvac: Common Services user filter + distribution list alongside separate email ems-backend#1262
• Please insert any useful link ( documentation you used for example )

Type of change

• New feature (non-breaking change which adds functionality)
• Improvement (refactor or addition to existing functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

• Test A
• Test B

Screenshots

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Checklist:

( * == Mandatory )

• * I have set myself as assignee of the pull request
• * My code follows the style guidelines of this project
• * Linting does not generate new warnings
• * I have performed a self-review of my own code
• * I have put the ticket for review, adding the oort-frontend team to the list of reviewers
• * I have commented my code, particularly in hard-to-understand areas
• * I have put JSDoc comment in all required places
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• * I have included screenshots describing my changes if relevant
• * I have selected labels in the Pull Request, according to the changes with code brings
• I have made corresponding changes to the documentation ( if required )
• I have added tests that prove my fix is effective or that my feature works
• * New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules