feature request: Set http client

[dennypenta]

What problem did you meet?

Injecting a http client as a dependency is necessary for observability and the others purposes.
For instance, in order to send a trace to OTLP trace provider we have to use our implementation of http.Client with custom http.Transport.

Describe what you'd like Logto to have

There are following options to achieve it:

• Add functional option pattern in order to keep the interface compatible, here is the good explanation: https://golang.cafe/blog/golang-functional-options-pattern.html, it can look the following:

func WithHttpClient(c *http.Client) func(*LogtoClient) {
  return func(logtoClient *LogtoClient) {
    logtoClient.httpClient = c
  }
}

• Add a setter for http.Client, In my opinion it shouldn't be thread safe, the client must be instantiate on the dependencies build step

func (logtoClient *LogtoClient) SetHttpClient(c *http.Client) {
  logtoClient.httpClient = c
}

[xiaoyijun]

Hi @dennypenta , thanks for your feedback, I will take a look.