We should ignore java.io.tmpdir and override it with ES_TMPDIR. I think that variable should be taken into account from the beginning of startup scripts (including JavaVersionChecker) and the value should be applied as java option to all java processes.

Java processes started before ES_JAVA_OPTS are parsed (JavaVersionChecker, TempDirectory, JvmOptionParser) can also create temporary files in /

This is kind of a follow up to #32677 and the PR #34762.

In #34762 we improved the test data source implementation by checking the body of the response from Tempo. The Tempo team is not comfortable making the body of a 404 response part of our stable API, so instead we are currently adding a separate endpoint specifically for testing: /api/echo (grafana/tempo#714).

When user choose date histogram function for x-xis column, we should auto populate the field with index pattern default time field.

it will save user lots of clicks

Lens already does it when we drag field into main view, it also doesn't do it if we drag field into column in layer view

![image](https://user-images.githubusercontent.com/3505601/123105411-1590cb80-d438-11eb-873b-d49259e66d

As suggested in the ESM guidelines of Node.js it would be good to explicit the type of the module.

{
+  "type": "commonjs",
}