[Maps] add in product help for layer group drag and drop instructions

[nreese]

Follow up to #142528

Drag and drop features can be hard to discover. This PR adds some in product help that describes how to use drag and drop to add and remove layers from a layer group.

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)

[gchaps]

Here's a suggestion:

Drag layers in and out of the group

• To add your first layer, drag it onto the group name.
• To add another layer, drag it anywhere above the last group layer.
• To remove a layer, drag it above or below the group.

Question: Is it clear to users that they populate the group in the Layers list? Or should we add that wording in the write-up above?

If you just was want a simple feature announcement:

Drag layers in and out of the group in the Layers list.

[nickpeihl]

code and UI changes lgtm!

I also agree with @gchaps suggestions for improving the text.

Drag layers in and out of the group in the Layers list.

👍

[nreese]

@elasticmachine merge upstream

[gchaps]

What do you think about "Drag layers in and out of the group" for the title?

[nreese]

yes, lets use that title.

[gchaps]

LGTM with a few minor comments

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 7c79756

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
maps	2.7MB	2.7MB	+884.0B

Unknown metric groups

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
fleet	57	63	+6
osquery	103	108	+5
securitySolution	439	443	+4
total			+17

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
fleet	65	71	+6
osquery	104	110	+6
securitySolution	516	520	+4
total			+18

History

• 💚 Build #84427 succeeded b70379e
• 💚 Build #84124 succeeded ce6f28a

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@elasticmachine merge upstream