[Feature] Support Synonyms API

[atsushi-matsui]

Is your feature request related to a problem? Please describe.
The Synonyms API has been GA in Elastic Search 8.13.
I want to support this API in Terraform.

Describe the solution you'd like
I want to create "ec_elasticsearch_ synonyms" as a new resource. This resource reads common synonym files such as the ones below, converts them to the Synonyms API format, and executes create/update requests.

hello, hi
bye, goodbye
test => check

Also, add an option called "synonym" to "elasticstack_elasticsearch_index", and if the resource ID of "ec_elasticsearch_ synonyms" is specified, I would like to execute the Reload search analyzers API to automatically reflect the contents of the dictionary in the index.

Additional context
To reflect new synonyms in an existing document, you need to update the document by running something like reindex.
I would like to add this to the documentation as a note.