Support EXACT operator in filters

[nyurik]

Query bar supports EXACT operator, e.g. lang=ru and lang=(ru,fr), but the filter boxes only use the default EQ operator - producing lang:ru which matches both ru and ruo.

Two possible solutions:

• Add operator ?: OperatorType -- there could be usecases for other operators like lt -- e.g. options list preset well known values like 25%, 50%, and selecting it produces field<0.25.
• Add exactMatch ?: boolean parameter to the FieldValueSelectionFilterConfigType, with default set to false -- not as flexible approach.

Note that ast.addOrFieldValue already supports operator as the 4th optional param, so all that's needed would be to pass it.

Relevant code:

eui/src/components/search_bar/filters/field_value_selection_filter.tsx

Line 49 in fa2916e

export interface FieldValueSelectionFilterConfigType {

eui/src/components/search_bar/query/ast.ts

Lines 388 to 392 in 43ccf53

	addOrFieldValue(
	field: string,
	value: Value,
	must = true,
	operator: OperatorType = Operator.EQ

P.S. for now just a community project, low priority unless needed by some Elastic project