Add capabilty to inject custom fields in requests

[alexandrebouthinon]

What does this PR do?

Add capabilty to inject custom fields in requests. According to #245

How should this be manually tested?

I used this little program to test this new feature:

package main

import (
	"log"
	"os"

	"github.com/kuzzleio/sdk-go/kuzzle"
	"github.com/kuzzleio/sdk-go/protocol/websocket"
	"github.com/kuzzleio/sdk-go/types"
)

func main() {
	// Creates a WebSocket connection.
	// Replace "kuzzle" with
	// your Kuzzle hostname like "localhost"
	c := websocket.NewWebSocket("localhost", nil)
	// Instantiates a Kuzzle client
	kuzzle, _ := kuzzle.NewKuzzle(c, nil)
	// Connects to the server.
	err := kuzzle.Connect()
	if err != nil {
		log.Fatal(err)
		os.Exit(1)
	}
	ch := make(chan *types.KuzzleResponse)
	options := types.NewQueryOptions()

	query := types.KuzzleRequest{}
	query.AddCustomArg("cert", "cert")
	query.AddCustomArg("foo", "bar")

	go kuzzle.Query(&query, options, ch)
	<-ch

	// Disconnects the SDK
	kuzzle.Disconnect()
}

But it's very hard to check the WebSocket message so I used Wireshark:

[Tommy647]

Looks good to me

[codecov]

Codecov Report

Merging #246 into 2-dev will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            2-dev     #246      +/-   ##
==========================================
+ Coverage   88.86%   88.91%   +0.05%     
==========================================
  Files         244      244              
  Lines        4463     4466       +3     
==========================================
+ Hits         3966     3971       +5     
+ Misses        443      441       -2     
  Partials       54       54

Impacted Files	Coverage Δ
kuzzle/query.go	59.45% <100%> (+1.71%)	⬆️
realtime/subscribe.go	76.47% <0%> (+5.88%)	⬆️

---

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[Aschen]

Good job 👍 Just a few suggestions on API names
And also for the label, it's more an enhancement to me (or even a bugfix) rather than a new feature

[Aschen]

In our terminology we call these top level query fields "args" because you can then find them in the request.input.args property.
Maybe a method like AddArg would be more appropriate

[Aschen]

Same remark as for AddCustomField, something like CustomArgs

[codecov-io]

Codecov Report

Merging #246 into 2-dev will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            2-dev     #246      +/-   ##
==========================================
+ Coverage   88.86%   88.91%   +0.05%     
==========================================
  Files         244      244              
  Lines        4463     4466       +3     
==========================================
+ Hits         3966     3971       +5     
+ Misses        443      441       -2     
  Partials       54       54

Impacted Files	Coverage Δ
kuzzle/query.go	59.45% <100%> (+1.71%)	⬆️
realtime/subscribe.go	76.47% <0%> (+5.88%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 31ac1ec...082b018. Read the comment docs.