JSON Merge-Patch

I wanted to request that you all consider implementing a "merge" or
"update" function for performing in-place updates of JSON data-structures.

The relevant algorithm is described here:
https://tools.ietf.org/html/rfc7396

SQLite's json1 extension has an implementation and it's quite useful:
https://www.sqlite.org/cgi/src/artifact/3f017d2659e531d0

For example:

{k1: {x1: y1}} merge {k1: {x2: y2}} -- yields --> {k1 : {x1: y1, x2: y2}}

Thank you for all your work on Postgres. I hope you'll consider adding this
as a built-in function.

Charles