chore(server): count calls to GitHub for static resources as metric (#2166)

Part of
#2160.

Thanks to this, we'll be able to assess the load on GitHub, and perhaps
come up with reasons why the server has been unstable.

This PR only deals with static resources. Fetching versions via API will
be covered in another PR.

Author: krzema12

jit-binding-server/src/main/kotlin/io/github/typesafegithub/workflows/jitbindingserver/Main.kt

@@ -12,6 +12,8 @@ import io.github.typesafegithub.workflows.mavenbinding.buildVersionArtifacts
 import io.github.typesafegithub.workflows.shared.internal.getGithubAuthToken
 import io.ktor.client.HttpClient
 import io.ktor.client.engine.cio.CIO
+import io.ktor.client.plugins.HttpSend
+import io.ktor.client.plugins.plugin
 import io.ktor.http.HttpStatusCode
 import io.ktor.server.application.Application
 import io.ktor.server.application.ApplicationCall
@@ -66,7 +68,19 @@ fun Application.appModule(
     buildPackageArtifacts: suspend (ActionCoords, String, (Collection<ActionCoords>) -> Unit) -> Map<String, String>,
     getGithubAuthToken: () -> String,
 ) {
-    val httpClient = HttpClient(CIO)
+    val httpClient =
+        HttpClient(CIO).apply {
+            plugin(HttpSend).intercept { request ->
+                if (request.url.host == "raw.githubusercontent.com") {
+                    val counter =
+                        prometheusRegistry.counter(
+                            "calls_to_github",
+                        )
+                    counter.increment()
+                }
+                execute(request)
+            }
+        }
     val bindingsCache = buildBindingsCache(buildVersionArtifacts, httpClient)
     val metadataCache = buildMetadataCache(bindingsCache, buildPackageArtifacts, getGithubAuthToken)
     installPlugins(prometheusRegistry)