[exporter/opensearchexporter] add logstashFormat config to opensearch

[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.

[ps48]

Thanks for the PR @sw90lee. I didn't see this PR and have something similar raised for Dynamic index support in OS exporter: #40530. Do you mind taking a look at it, we can coordinate how to move ahead here. Thanks again!