T6671: defer config dependency if scheduled in priority queue

[jestabro]

Change Summary

If a config dependency is scheduled to run later in the priority queue, defer instead of running immediately from the source script of the dependency. This avoids running a script too early, if it will require the result of an intermediate script in the priority order. For example:

            dep
conntrack  ---->  conntrack-sync
   prio \            / prio
      interfaces_bonding

This becomes evident in 1.4 on boot with a suitable configuration, given the presence of the default conntrack modules entries (resolved in 1.5 for new installs; T3275). However, it indicates a general issue, which has a simple resolution in this PR.

Note that this is not apparent in 1.4.0, as there was a earlier pruning mechanism in place for config dependency scripts; that had to be dropped given other issues (T6559; also due to conntrack modules, which provides a useful canary given its low priority) and replaced by a smarter approach in this PR.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

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How to test

Smoketest added in PR.

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Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

👍
No issues in PR Title / Commit Title

[github-actions]

✅ No issues found in unused-imports check.. Please refer the workflow run

[jestabro]

@Mergifyio backport circinus sagitta

[mergify]

backport circinus sagitta

✅ Backports have been created

• #4016 T6671: defer config dependency if scheduled in priority queue (backport #4015) has been created for branch circinus
• #4017 T6671: defer config dependency if scheduled in priority queue (backport #4015) has been created for branch sagitta

[jestabro]

Force pushed to move copyright year update to correct commit; no substantive change.