Mention the 'indexing' settings in the SHRED_DOC_LIMIT_VIOLATION error message when due to inserted text exceeding indexable length

[sl-at-ibm]

Inserting, into a collection, a document with a text longer than ~8K chars for an indexed field errors with this:

"Document size limitation violated: indexed String value (field 'content') length (10538 bytes) exceeds maximum allowed (8000 bytes)","errorCode":"SHRED_DOC_LIMIT_VIOLATION"

This is due to the SAI index not able to (and not designed to!) accept very long strings.
The error message could be changed to mention/refer/link to the "indexing" option, as a better guidance to the user.

Caveat:

• the indexing can be changed only at creation time, so the user should be informed this requires a restart from scratch/reingestion or such.