[6.7] Using POST instead of DELETE for bulk deletion of pipelines (#31023) (#31205)

Backports the following commits to 6.7:
 - Using POST instead of DELETE for bulk deletion of pipelines  (#31023)

x-pack/plugins/logstash/public/services/pipelines/pipelines_service.js

@@ -80,14 +80,10 @@ export class PipelinesService {
    * @return Promise { numSuccesses, numErrors }
    */
   deletePipelines(pipelineIds) {
-    // $http.delete does not take the request body as the 2nd argument. Instead it expects the 2nd
-    // argument to be a request options object, one of which can be the request body (data). We also
-    // need to explicitly define the content type of the data.
-    const requestOpts = {
-      data: { pipelineIds },
-      headers: { 'Content-Type': 'application/json' }
+    const body = {
+      pipelineIds
     };
-    return this.$http.delete(`${this.basePath}/pipelines`, requestOpts)
+    return this.$http.post(`${this.basePath}/pipelines/delete`, body)
       .then(response => {
         this.addToRecentlyDeleted(...pipelineIds);
         return response.data.results;

x-pack/plugins/logstash/server/routes/api/pipelines/register_delete_route.js

@@ -37,8 +37,8 @@ export function registerDeleteRoute(server) {
   const licensePreRouting = licensePreRoutingFactory(server);
 
   server.route({
-    path: '/api/logstash/pipelines',
-    method: 'DELETE',
+    path: '/api/logstash/pipelines/delete',
+    method: 'POST',
     handler: (request) => {
       const callWithRequest = callWithRequestFactory(server, request);
 

x-pack/test/api_integration/apis/logstash/pipelines/delete.js

@@ -30,8 +30,8 @@ export default function ({ getService }) {
 
     it('should delete the specified pipelines', async () => {
       await supertest
-        .delete(
-          '/api/logstash/pipelines'
+        .post(
+          '/api/logstash/pipelines/delete'
         )
         .set('kbn-xsrf', 'xxx')
         .send({