Prometheus: Introduce prometheus backend library (#83952)

* Move files to prometheus-library

* refactor core prometheus to use prometheus-library

* modify client transport options

* mock

* have a type

* import aliases

* rename

* call the right method

* remove unrelated test from the library

* update codeowners

* go work sync

* update go.work.sum

* make swagger-clean && make openapi3-gen

* add promlib to makefile

* remove clilogger

* Export the function

* update unit test

* add prometheus_test.go

* fix mock type

* use mapUtil from grafana-plugin-sdk-go

pkg/promlib/client/transport.go

@@ -0,0 +1,49 @@
+package client
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	sdkhttpclient "github.com/grafana/grafana-plugin-sdk-go/backend/httpclient"
+	"github.com/grafana/grafana-plugin-sdk-go/data/utils/maputil"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend/log"
+
+	"github.com/grafana/grafana/pkg/promlib/middleware"
+	"github.com/grafana/grafana/pkg/promlib/utils"
+)
+
+// CreateTransportOptions creates options for the http client.
+func CreateTransportOptions(ctx context.Context, settings backend.DataSourceInstanceSettings, logger log.Logger) (*sdkhttpclient.Options, error) {
+	opts, err := settings.HTTPClientOptions(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("error getting HTTP options: %w", err)
+	}
+
+	jsonData, err := utils.GetJsonData(settings)
+	if err != nil {
+		return nil, fmt.Errorf("error reading settings: %w", err)
+	}
+	httpMethod, _ := maputil.GetStringOptional(jsonData, "httpMethod")
+
+	opts.Middlewares = middlewares(logger, httpMethod)
+
+	return &opts, nil
+}
+
+func middlewares(logger log.Logger, httpMethod string) []sdkhttpclient.Middleware {
+	middlewares := []sdkhttpclient.Middleware{
+		// TODO: probably isn't needed anymore and should by done by http infra code
+		middleware.CustomQueryParameters(logger),
+		sdkhttpclient.CustomHeadersMiddleware(),
+	}
+
+	// Needed to control GET vs POST method of the requests
+	if strings.ToLower(httpMethod) == "get" {
+		middlewares = append(middlewares, middleware.ForceHttpGet(logger))
+	}
+
+	return middlewares
+}