Enhance Elasticsearch String field mapping

[OmarHawk]

Fix #29311

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[OmarHawk]

This change produces problems when having String fields exceeding the max length of keywords (e.g. TextBlob or String with maxlength > 256). In that case, the contents cannot be indexed anymore. So, I converted this PR back to a Draft.

[OmarHawk]

I've added another param to the annotation that fixes the issue with String contents > 256 characters - this is also part of the standard mapping, and I had missed that out before

[mshima]

@OmarHawk we are a few days from v9 beta.
Do you think we should include in v8?

[OmarHawk]

@OmarHawk we are a few days from v9 beta. Do you think we should include in v8?

No, this PR goes rather into the 'better developer experience' and is not a bugfix per se. So, I think, we don't need it in v8.