feat: allow passing custom http client

[ngoduykhanh]

Eppo Internal:

🎟️ Fixes #74
📜 Design Doc: link if applicable

Motivation and Context

To allow tuning the HTTP client, such as TCP transportation config, to fix the issue reported in #74.

Description

With this change, when we initialize the Eppo client, we can pass in a custom HTTP client like this:

		var httpClientInstance *http.Client
		httpClientInstance = &http.Client{Timeout: 10 * time.Second}
		httpClientInstance.Transport = &http.Transport{
			Proxy: http.ProxyFromEnvironment,
			DialContext: (&net.Dialer{
				Timeout:   5 * time.Second,
				KeepAlive: 10 * time.Second,
			}).DialContext,
			MaxIdleConns:          100,
			IdleConnTimeout:       90 * time.Second,
			TLSHandshakeTimeout:   10 * time.Second,
			ExpectContinueTimeout: 1 * time.Second,
			ForceAttemptHTTP2:     true,
		}

		config := eppoclient.Config{
			SdkKey:            os.Getenv("EPPO_SDK_KEY"),
			PollerInterval:    5 * time.Second,
			ApplicationLogger: customLogger,
			HttpClient:        httpClientInstance,
		}

This parameter is optional, and if we don't specify it, the default behavior will be applied.

With the above config, the netstat output will look like this, where we have multiple TCP connection rotated.

/app $ netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:43202 151.101.65.91:https     ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:44978 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:58722 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:50592 151.101.193.91:https    ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:58724 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:34132 151.101.129.91:https    ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:38196 151.101.193.91:https    ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:32936 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:44244 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:39742 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:42666 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:55332 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:43618 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:42682 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:39740 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:55334 151.101.1.91:https      ESTABLISHED
tcp        0      0 test-eppo-698b9bdcfd-8bjhf:44228 151.101.1.91:https      ESTABLISHED

How has this been documented?

How has this been tested?

[leoromanovsky]

Thanks for the PR! Good luck with the tuning - if you find an improvement would you be able to share?

[ngoduykhanh]

Hey @leoromanovsky, thanks for reviewing. Yes, I can give an update when we roll out the changes. Could you please have another release after merging this PR? It seems like I cannot merge the PR by myself.

[leoromanovsky]

Hey @leoromanovsky, thanks for reviewing. Yes, I can give an update when we roll out the changes. Could you please have another release after merging this PR? It seems like I cannot merge the PR by myself.

Published as https://github.com/Eppo-exp/golang-sdk/releases/tag/v6.2.0