Improve errors shown in the ES|QL editor for incomplete queries

[teresaalvarezsoler]

Description

Incomplete queries throw incomprehensible errors (see below).

Can I suggest a template like the following?
Syntax error: after a <mention the last element written> within <mention the last function after the last pipe if it exists> you usually need <mention up to 2 alternatives>

Examples:

• The below error will become this: Syntax error: after a pipe '|' you usually need a a function like 'STATS' or 'WHERE'
• The below error will become this: Syntax error: after a comma ',' within a 'KEEP' function you usually need a field name