[Docs] Clarify behaviour of Pattern Capture Token Filter during search

There was some confusion about the fact that tokens emitted from a Pattern
Capture Token Filter are treated as synonyms when used to analyze a search
query. This commit adds an explanation to the note in the docs to emphasize this
behaviour.

Closes elastic#25746

Author: cbuescher

docs/reference/analysis/tokenfilters/pattern-capture-tokenfilter.asciidoc

@@ -147,3 +147,7 @@ not:
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   john-<em>smith</em>[email protected]
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+
+When used to analyze a search query, all tokens emitted by the filter
+are going to be treated as synonyms of the token in the original position,
+so any of those tokens will be considered as a match candidate.