Index pattern creation UX: Improve explanatory copy

[cjcenizal]

Clarify "Do not expand index pattern" explanatory text

Taken from #9991 (comment):

When the option is checked, two very similar messages are visible, but one is treated as a "notification" and the other is just regular text. When I read these two messages, it's hard for me to figure out which one applies to the checked state. I think this is partially because a) the notification treatment obscures the fact that the two messages are two sides of the same coin and b) the second message is broken up into two paragraphs, and the second paragraph makes a statement that doesn't apply to the checked state but doesn't make this clear.

I think we can fix this by removing the notification treatment, and adjusting the copy to clearly identify what happens when the option is selected and not selected. Let's change this copy and keep all of it visible regardless of whether the option is checked or not:

With this option not selected, searches against any time-based index pattern that contains a wildcard will automatically be expanded to query only the indices that contain data within the currently selected time range. Searching against the index pattern logstash-* will actually query elasticsearch for the specific matching indices (e.g. logstash-2015.12.21) that fall within the current time range.

With this option selected, this index pattern will be queried directly rather than being expanded into more performant searches against individual indices. Elasticsearch will receive a query against logstash-* and will have to search through all matching indices regardless of whether they have data that matches the current time range.

FYI, if you or anyone decides to massage this copy further, this comment #8128 (comment) has some suggestions on how it should be rephrased.

[cjcenizal]

@alexfrancoeur Could you add more copy-improvement notes to this isuse?

[cjcenizal]

Per @bohyun-e We need better explanatory copy and documentation in general for this flow. Feel free to add additional details, Bohyun.

[cjcenizal]

Note: the "do not expand" explanatory copy will be removed entirely by #10445.

[cjcenizal]

Addressed by #13454