Add support for dual reads in mongobetween

[kounat]

This PR adds support for dual reads, which allows us to make reads to a migrated cluster and verify performance/correctness in a way that is invisible to the application.

The second round trip is made after the socket write and the client should see no change in latency with dual reads enabled.

[ThatHurleyGuy]

Just making a note so I remember where I'm at. I was starting my stress testing and saw some panics from this line of code:

{"level":"error","ts":1653593508.0804174,"caller":"proxy/connection.go:35","message":"Connection crashed","remote_address":"@","panic":"Call of bsoncore.Value.Document on invalid type","stack":"goroutine 267 [running]:\nruntime/debug.Stack()\n\t/usr/local/Cellar/go/1.17.2/libexec/src/runtime/debug/stack.go:24 +0x65\ngithub.com/coinbase/mongobetween/proxy.handleConnection.func1()\n\t/Users/sean.hurley/workspace/mongobetween/proxy/connection.go:35 +0xc7\npanic({0xbd8e00, 0xc0010418d8})\n\t/usr/local/Cellar/go/1.17.2/libexec/src/runtime/panic.go:1038 +0x215\ngo.mongodb.org/mongo-driver/x/bsonx/bsoncore.Value.Document({0x75, {0x0, 0xc, 0xc00192f6e8}})\n\t/Users/sean.hurley/go/pkg/mod/go.mongodb.org/mongo-driver@v1.8.0/x/bsonx/bsoncore/value.go:443 +0x15f\ngithub.com/coinbase/mongobetween/mongo.MustOpMsgCursorSection({0xe38c90, 0xc000f72bd0})\n\t/Users/sean.hurley/workspace/mongobetween/mongo/operations.go:363 +0xaa\ngithub.com/coinbase/mongobetween/proxy.(*connection).roundTripWithDualCursor(0xc00192fed8, 0xc000b9cab0, 0xc000b9cd80, 0x0, {0xc0006354a0, 0x6, 0xa})\n\t/Users/sean.hurley/workspace/mongobetween/proxy/connection.go:229 +0x874\ngithub.com/coinbase/mongobetween/proxy.(*connection).handleMessage(0xc00192fed8)\n\t/Users/sean.hurley/workspace/mongobetween/proxy/connection.go:136 +0xc25\ngithub.com/coinbase/mongobetween/proxy.(*connection).processMessages(0xc00192fed8)\n\t/Users/sean.hurley/workspace/mongobetween/proxy/connection.go:55 +0x3d\ngithub.com/coinbase/mongobetween/proxy.handleConnection(0x0, 0xc6626f, {0xc00007a540, 0x0}, {0xe37700, 0xc00000e180}, 0x0, 0x0, 0x0)\n\t/Users/sean.hurley/workspace/mongobetween/proxy/connection.go:50 +0xd1\ngithub.com/coinbase/mongobetween/proxy.(*Proxy).accept.func2()\n\t/Users/sean.hurley/workspace/mongobetween/proxy/proxy.go:165 +0xae\ncreated by github.com/coinbase/mongobetween/proxy.(*Proxy).accept\n\t/Users/sean.hurley/workspace/mongobetween/proxy/proxy.go:163 +0x368\n"}

Will need to dig in more as to why that's happening (Looks like we're assuming ALL reads have a cursor in the response, but might not be the case

[ThatHurleyGuy]

Add a little more logging to see what the op looked like when this error is happening:

{ OpMsg flags: 0, sections: [{ SectionSingle msg: {"ok": {"$numberDouble":"0.0"},"errmsg": "No keys found for HMAC that is valid for time: { ts: Timestamp(1653595159, 1562) } with id: 7102116512885899268","code": {"$numberInt":"211"},"codeName": "KeyNotFound","$clusterTime": {"clusterTime": {"$timestamp":{"t":"1653595159","i":"1561"}},"signature": {"hash": {"$binary":{"base64":"Nthr9PHRWcpILtOPqyful0plsf8=","subType":"00"}},"keyId"
: {"$numberLong":"7102116560130539524"}}},"operationTime": {"$timestamp":{"t":"1653595159","i":"1561"}}} }], checksum: 0 }

Will dig in more later

[kounat]

Closing in favor of #51