<!-- Add the related story/sub-task/bug number, like Resolves#123, or
remove if NA -->
**Related issue:** Resolves
https://fleetdm.slack.com/archives/C03C41L5YEL/p1761232938314509, but
also https://github.com/fleetdm/fleet/issues/34363, as it would have
been stupid to only add IDP_USERNAME (to allow for an email) when they
are so close together and no extra effort to support the rest.
Also does another fix to ensure fleet variables are correctly ordered by
longest name to shortest, to ensure variables that are used in longer
format (USERNAME, USERNAME_LOCAL_PART) that the LOCAL_PART one gets
processed first.
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
## Testing
- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually
<!-- Add the related story/sub-task/bug number, like Resolves#123, or
remove if NA -->
**Related issue:** Resolves#33502
This fixes the mentioned issue by always sorting the found variables in
length descending, to ensure we process the longest variables first,
avoiding us processing a smaller variation of a longer variable first
breaking substitution.
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.
## Testing
- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually
