T7499: bindings for (non-)destructive configtree merge

[jestabro]

Change summary

Binding for merge function ; draft pending merge of:
vyos/vyos1x-config#45
vyos/vyconf#24
at which point the commit refs will be updated in build.sh and the PR opened.

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)

Checklist:

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