Alerting: Remove the POST endpoint for the internal Grafana Alertmanager config (#103819)

* Remove POST config for Grafana Alertmanager

* Delete auth + test for removed path

* Alerting: Remove check for `alertingApiServer` toggle in UI (#103805)

* Remove check for alertingApiServer in UI

* Update tests to no longer care about alertingApiServer

* Add contact points handlers now that we use alertingApiServer all the time

* Fix test broken from removing camelCase for UIDs

---------

Co-authored-by: Tom Ratcliffe <tom.ratcliffe@grafana.com>

pkg/tests/api/alerting/testing.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -420,40 +419,6 @@ func (a apiClient) UpdateAlertRuleOrgQuota(t *testing.T, orgID int64, limit int6
 	assert.Equal(t, http.StatusOK, resp.StatusCode)
 }
 
-func (a apiClient) PostConfiguration(t *testing.T, c apimodels.PostableUserConfig) (bool, error) {
-	t.Helper()
-
-	b, err := json.Marshal(c)
-	require.NoError(t, err)
-
-	u := fmt.Sprintf("%s/api/alertmanager/grafana/config/api/v1/alerts", a.url)
-	req, err := http.NewRequest(http.MethodPost, u, bytes.NewReader(b))
-	require.NoError(t, err)
-	req.Header.Set("Content-Type", "application/json")
-
-	client := &http.Client{}
-	resp, err := client.Do(req)
-	require.NoError(t, err)
-	require.NotNil(t, resp)
-
-	defer func() {
-		_ = resp.Body.Close()
-	}()
-	b, err = io.ReadAll(resp.Body)
-	require.NoError(t, err)
-
-	data := struct {
-		Message string `json:"message"`
-	}{}
-	require.NoError(t, json.Unmarshal(b, &data))
-
-	if resp.StatusCode == http.StatusAccepted {
-		return true, nil
-	}
-
-	return false, errors.New(data.Message)
-}
-
 func (a apiClient) PostRulesGroupWithStatus(t *testing.T, folder string, group *apimodels.PostableRuleGroupConfig, permanentlyDelete bool) (apimodels.UpdateRuleGroupResponse, int, string) {
 	t.Helper()
 	buf := bytes.Buffer{}