[ES|QL] Improve initial empty state

[ryankeairns]

Describe the feature:
Currently, an error message is present when the editor is empty. This means all new queries begin with an error warning.
Instead, we could suppress the error/validation check and, alternatively, show either placeholder text or an initial suggestion once the user enters (focuses) on the editor.

Describe a specific use case for the feature:

1. The editor start in an empty state with no error message.
2. User tabs or clicks into the empty editor.
3. An autocomplete suggestion appears suggesting to write from, row, or show. Technically, they can type anything, but this seems the most common, logical starting point for a new query.

[elasticmachine]

Pinging @elastic/kibana-esql (Team:ESQL)

[stratoula]

@ryankeairns also it would be nice to think how an empty state will look in discover. Currently if the user submits an empty query we error out (as we are sending the request at ES and query is a mandatory field)

Ideas:

• Not allow submitting an empty query
• Allow the submission but show no error but a nice empty state instead
• More...

[stratoula]

This has been partially been addressed. Now we don't error out on an empty query

[ryankeairns]

Closing this given the partial resolution. Will open a new issue once design is ready.