Replace `json-schema-merge-allof` dependency

[x0k]

Problem

• The library is unmaintained
• Has questionable performance (related)
• Depends on lodash (basic-starter bundle analysis, json-schema-merge-allof + lodash: 216kb rendered, 92kb gzip)

Suggested solution

• Consider similar solutions (allof-merge)
• Develop in house solution to support our use cases (modularity, no external dependencies)

[x0k]

Results:

• 19kb rendered, 4.4kb gzip (in minimal variant)
• 10x-50x faster than json-schema-merge-allof, 2x-20x faster than allof-merge
• Getting rid of dependency, full control over the code