Feature client transport config

[FriMeDev]

What kind of change does this PR introduce?

Add the possibility to define custom transport settings for the http.Client. Furthermore the renaming prevents stuttering (former Client.clientTransport)

What is the current behavior?

Any information can be found in #39

What is the new behavior?

It is now possible to define custom transport behavior by setting Client.Transport.Parent:

func main() {
	c := postgrest.NewClient("localhost:3000", "", nil)

	c.Transport.Parent = &http.Transport{
		TLSClientConfig: &tls.Config{
			RootCAs:            x509.NewCertPool(),
			InsecureSkipVerify: false,
		},
	}
}

Additional information

Due to the behavior of httpmock used for testing, the implemented RoundTrip() is not as clean as it could be. For testing with httpmock to work properly http.DefaultTransport.RoundTrip() must be called in RoundTrip() in client.go.

[tranhoangvuit]

Hi @Fritte795, it looks good to me, but could you please resolve the conflict first?

[muratmirgun]

@tranhoangvuit I will fix this conflicts tonight

[elijahmorg]

This PR clobbered the changes made in #41

In current main you cannot set apikey and token separately.