CDRIVER-4363 add nsInfo builder

[kevinAlbs]

Summary

This PR adds a private component to build the nsInfo payload for CDRIVER-4363. No publicly visible changes are expected.

• Add private type mcd_nsinfo_t to build the nsInfo payload in the bulkWrite command.
• Add uthash 2.3.0.

Background & Motivation

The mcd_nsinfo_t is intended for upcoming support of the bulkWrite command. Each operation in a bulkWrite references an int32 index into an array of unique namespaces:

{
    "bulkWrite": 1,
    "ops": [
        {
            "insert": 0, # references 'db.coll1'
            "document": { "_id": "foo" }
        },
        {
            "insert": 0, # references 'db.coll1'
            "document": { "_id": "bar" }
        },
        {
            "insert": 1, # references 'db.coll2'
            "document": { "_id": "baz" }
        }
    ],
    "nsInfo": [
        { "ns": "db.coll1" },
        { "ns": "db.coll2" }
    ]
}

The syntax of the bulkWrite command is further described in Scope: Server improved bulk write command.

Each operation can refer to a different namespace. There can be up to maxWriteBatchSize operations in one command. The server currently defines maxWriteBatchSize in the response to the hello command as 100,000.

My initial implementation stored a map of namespace to int32 in a bson_t and did linear look-up. This resulted in an O(n^2) algorithm which took very long to execute for a large number of namespaces (I stopped waiting after several minutes).

A hash table with faster look-up seemed needed. uthash was chosen for simplicity (small header-only library) and consistency with other dependencies used (utlist.h is already copied).

[kevinAlbs]

Thank you for the suggestions.

utlist.h has also been updated to 2.3.0.

Patch build to verify: https://spruce.mongodb.com/version/662bc956c099380007552450