Revert timestamp changes in the /api/infra/metrics_explorer API (elas…

…tic#178125)

Closes elastic#171742

## Summary

- Revert timestamp changes related to
https://github.com/elastic/kibana/pull/162542/files#r1275851279
- Removed unused files related to previous preview charts

## 🧪 How to test
Please check this PR carefully!
- Create a custom threshold rule as described
[here](https://github.com/elastic/kibana/blob/main/x-pack/plugins/observability_solution/observability/dev_docs/custom_threshold.md)
and verify:
    - The preview chart in the rule flyout is working as expected
    -  On the alert details page, charts are shown correctly
- In the infra plugin, make sure
    - Metric explorer page works as before
- If you know of any other usage for `/api/infra/metrics_explorer`
please check those as well

x-pack/plugins/observability_solution/infra/common/http_api/metrics_api.ts

@@ -8,18 +8,7 @@
 import { createLiteralValueFromUndefinedRT } from '@kbn/io-ts-utils';
 import * as rt from 'io-ts';
 import { MetricsUIAggregationRT } from '@kbn/metrics-data-access-plugin/common';
-import { afterKeyObjectRT } from './metrics_explorer';
-
-export const MetricsAPITimerangeRT = rt.intersection([
-  rt.type({
-    from: rt.number,
-    to: rt.number,
-    interval: rt.string,
-  }),
-  rt.partial({
-    timeFieldName: rt.string,
-  }),
-]);
+import { afterKeyObjectRT, timeRangeRT } from './metrics_explorer';
 
 const groupByRT = rt.union([rt.string, rt.null, rt.undefined]);
 
@@ -30,7 +19,7 @@ export const MetricsAPIMetricRT = rt.type({
 
 export const MetricsAPIRequestRT = rt.intersection([
   rt.type({
-    timerange: MetricsAPITimerangeRT,
+    timerange: timeRangeRT,
     indexPattern: rt.string,
     metrics: rt.array(MetricsAPIMetricRT),
     includeTimeseries: rt.union([rt.boolean, createLiteralValueFromUndefinedRT(true)]),
@@ -95,7 +84,7 @@ export const MetricsAPIResponseRT = rt.type({
   info: MetricsAPIPageInfoRT,
 });
 
-export type MetricsAPITimerange = rt.TypeOf<typeof MetricsAPITimerangeRT>;
+export type MetricsAPITimerange = rt.TypeOf<typeof timeRangeRT>;
 
 export type MetricsAPIColumnType = rt.TypeOf<typeof MetricsAPIColumnTypeRT>;
 

x-pack/plugins/observability_solution/infra/common/http_api/metrics_explorer.ts

@@ -74,16 +74,11 @@ export const metricsExplorerMetricRT = rt.intersection([
   metricsExplorerMetricOptionalFieldsRT,
 ]);
 
-export const timeRangeRT = rt.intersection([
-  rt.type({
-    from: rt.number,
-    to: rt.number,
-    interval: rt.string,
-  }),
-  rt.partial({
-    timeFieldName: rt.string,
-  }),
-]);
+export const timeRangeRT = rt.type({
+  from: rt.number,
+  to: rt.number,
+  interval: rt.string,
+});
 
 export const metricsExplorerRequestBodyRequiredFieldsRT = rt.type({
   timerange: timeRangeRT,

x-pack/plugins/observability_solution/infra/server/lib/metrics/index.ts

@@ -42,7 +42,7 @@ export const query = async (
   const filter: Array<Record<string, any>> = [
     {
       range: {
-        [options.timerange.timeFieldName || TIMESTAMP_FIELD]: {
+        [TIMESTAMP_FIELD]: {
           gte: options.timerange.from,
           lte: options.timerange.to,
           format: 'epoch_millis',

x-pack/plugins/observability_solution/infra/server/lib/metrics/lib/create_aggregations.ts

@@ -37,7 +37,7 @@ const createMetricHistogramAggs = (options: MetricsAPIRequest): HistogramAggrega
   return {
     histogram: {
       date_histogram: {
-        field: options.timerange.timeFieldName || TIMESTAMP_FIELD,
+        field: TIMESTAMP_FIELD,
         fixed_interval: intervalString,
         offset: options.alignDataToEnd ? calculateDateHistogramOffset(options.timerange) : '0s',
         extended_bounds: {