Add libicu version fetching and emit it in the _node/_local/_versions

[nickva]

Fetch the libicu base version as well as the collator version. The base version may be used to determine which libicu library CouchDB is using. The collator version may be used to debug view behavior in case when collation order had changed from one version to the next.

[jaydoane]

Slick!

$ curl -s -u adm:pass localhost:15984/_node/_local/_versions | jq .collation_driver
{
  "name": "libicu",
  "library_version": "69.1",
  "collation_algorithm_version": "13"
}