bindings: T6742: correct childless leaf nodes rendering

[dmbaturin]

Change Summary

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)
• Other (please describe):

Related Task(s)

Related PR(s)

• renderer: T6742: make childless non-leaf nodes from parsed configs render correctly vyos1x-config#30
• build-image: T6742: update vyos1x-config for childless non-leaf node rendering fixes vyos-build#774

Proposed changes

• New function for creating intermediate non-leaf nodes: create_node(tree, path).
• New functions for checking and setting leaf flags: is_leaf and set_leaf.
• Building against newer vyos1x-config will bring the childless non-leaf node rendering fix.

How to test

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

[sever-sever]

Fails to build

 ocamlc -g -c stub/init.c
mv init.o _build/stub/init.o
ocamlfind opt -c -o _build/lib/bindings.cmx -I _build/generated -I _build/lib -package vyos1x-config,re,ctypes.stubs,ctypes.foreign lib/bindings.ml
Warning: : [WARNING] Package `threads': Linking problems may arise because of the missing -thread or -vmthread switch
File "lib/bindings.ml", line 60, characters 21-35:
60 |         let new_ct = CT.create_node ct path in
                          ^^^^^^^^^^^^^^
Error: Unbound value CT.create_node
make[2]: *** [Makefile:64: _build/lib/bindings.cmx] Error 2
make[2]: Leaving directory '/__w/vyos-reusable-workflows/vyos-reusable-workflows/libvyosconfig'
make[1]: *** [debian/rules:9: override_dh_auto_build] Error 2
make[1]: Leaving directory '/__w/vyos-reusable-workflows/vyos-reusable-workflows/libvyosconfig'
make: *** [debian/rules:6: build] Error 2
dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2