Synonyms API - Add invalid synonyms information

[carlosdelest]

Description

When invalid synonyms are added to a synonym graph or synonym token filter and lenient is set to true, invalid synonyms are ignored.

The only indication for this are log messages , which are not immediate feedback to the user. These failures are returned as part of any API in Elasticsearch.

A way of detecting invalid synonyms configuration needs to be added to the Elasticsearch API, either in an existing one or as part of the Synonyms API.

Related:

• Gracefully handle invalid synonym rules in updateable synonyms #110901
• Synonyms API: Index gets red status when synonyms set does not exist #125603

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Pinging @elastic/es-search-relevance (Team:Search Relevance)

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Pinging @elastic/search-eng (Team:SearchOrg)

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Pinging @elastic/search-relevance (Team:Search - Relevance)