feat: client metrics

[monosoul]

Subsystem
Client

Motivation
Provide a plugin to instrument Ktor client similarly to how the server lib is instrumented with Micrometer.

Solution
This is basically just a PoC to discuss if the approach is okay or not. If it's okay, then I'll proceed with adding tests etc. If not, then we can discuss it here.

The idea here is to provide a client instrumentation similar to how it's done in OkHttpMetricsEventListener - introduce a timer for client requests.

The implementation is heavily inspired by the Logging plugin.

Since using an expanded URI as the value for the URI tag can lead to cardinality blow up, I had to introduce support for URI templates. This is done in 0e542bd. While those methods could potentially be added as extension functions in the plugin module, it feels like they belong to the core lib more.
( Probably a better option there would be to have a set of explicit builder functions like:

client.get(uriTemplate: String, vararg pathParameters: Pair<String, Any>, block: HttpRequestBuilder.() -> Unit = {})

Then it wouldn't be necessary to rebuild the URL. This is the path Spring followed with their client for example: https://github.com/spring-projects/spring-framework/blob/main/spring-web/src/main/java/org/springframework/web/client/RestTemplate.java#L400 )

The URI template is stored as a call attribute with the first call to HttpRequestBuilder.pathParameters and is later used in MicrometerMetrics plugin.

Here's how using the new methods would look like:

client.get("https://blog.jetbrains.com/kotlin/{year}/{month}/{name}/") {
    pathParameters(
         "year" to 2023,
         "month" to "11",
         "name" to "kotlin-1-9-20-released",
    )
}.bodyAsText()

The plugin is implemented in 2e9cab1 and provides configuration to make it flexible enough to cover most of the use cases.

The timer will be started when request has been sent and will be stopped either when an exception has occurred, or when the response has been received.

[e5l]

Hey @monosoul, thanks for the PR!

@marychatte, could you please check?

[marychatte]

Thanks a lot for the PR! And sorry for the big delay in the review
Good work, I like the idea of plugin. And I added some comments

[marychatte]

Can we remove url.build() here and make it call only once? Maybe we can use HttpRequestBuilder.attributes to save parameters and build later

[marychatte]

Why does it need to be saved as a String? Later, it's used to parse, but maybe we can use functions URL.encodedQuery or URL.encodedPath

[marychatte]

What about pathSegment = /{year}_{month}/ for example?

[marychatte]

We also replace query parameters here, so the names pathParameters(...) and pathParameter(...) can be confusing. And it's also better to add in example query parameter values for clarity

[marychatte]

We need to copy fragment and trailingQuery too

[marychatte]

Can you please add in Kdoc example of plugin usage?

[marychatte]

Can we extract it so it does not have copypaste?

[marychatte]

Can we add FailureHook so there is no need to write try-catch?

[marychatte]

Can we extract regex here so as not to compile it every time?

[marychatte]

Can we, instead of creating new Hooks, use functions onRequest {... }, onResponse {... } etc?