[exporter/opensearchexporter] add logstashFormat config to opensearch close

[sw90lee]

Description

OpenSearch currently lacks date suffixing for index names. To maintain consistency with the Elasticsearch Exporter, I implemented a similar configuration mechanism for OpenSearch and documented its usage in the README.md.

Link to tracking issue

#34746
#38595

Testing

Documentation

• logstash_format (optional): Logstash format compatibility. Logs, metrics and traces can be written into an index in Logstash format.
  • enabled(default=false): Enable/disable Logstash format compatibility. When logstash_format::enabled is true, the index name is composed using the above dynamic routing rules as prefix and the date as suffix,
    e.g: If the computed index name is logs-generic-default, the resulting index will be logs-generic-default-YYYY.MM.DD.
    The last string appended belongs to the date when the data is being generated.
  • prefix_separator(default=-): Set a separator between logstash_prefix and date.
  • date_format(default=%Y.%m.%d): Time format (based on strftime) to generate the second part of the Index name.

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