T6207: restore ability to copy config.boot.default on image install

[jestabro]

Change Summary

NOTE: this requires the companion PR vyos/vyos-build#551 to adjust the test script for added prompt.

The option to use config.boot.default was unfortunately dropped during development of the revised image-tools; this is a problem, for example, for EVE-NG installs:
https://www.eve-ng.net/index.php/documentation/howtos/howto-add-vyos-vyatta/

Restore option.

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):

Related Task(s)

Related PR(s)

vyos/vyos-build#551

Component(s) name

Proposed changes

How to test

Smoketest result

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

[c-po]

@Mergifyio backport sagitta

[mergify]

backport sagitta

✅ Backports have been created

• #3279 T6207: restore ability to copy config.boot.default on image install (backport #3278) has been created for branch sagitta