[DOC] Update List To Map Processor documentation to include delete source flag

[jack-hung-lgtm]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. A new flag "delete_source" has been added to the List To Map processor in the data prepper package. This flag determines whether the source key is deleted after the json fields are processed. My request is to add documentation for this flag in the existing List To Map Processor documentation.

Version: all

What other resources are available?

Page to add documentation: https://docs.opensearch.org/latest/data-prepper/pipelines/configuration/processors/list-to-map/.

Functionally, the delete_source flag results in the same behavior as described here for the Parse to Json processor: https://docs.opensearch.org/latest/data-prepper/pipelines/configuration/processors/parse-json/.

The PR that will add this change is here: opensearch-project/data-prepper#6297