[DOC] characterization. of eval command

[smacrakis]

What do you want to do?

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

Tell us about your request. Provide a summary of the request.

Page https://opensearch.org/docs/2.15/search-plugins/sql/ppl/functions/, under "eval", reads: "The eval command is not rewritten to OpenSearch DSL, it is only executed on the coordination node."

That is a description of the implementation which is meaningless to most users. What does this mean for the user?

*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.

2.15

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[hdhalter]

Thanks, @smacrakis, it looks like that sentence is used for all commands. @kolchfa-aws, do you know what is meant by this statement?

[kolchfa-aws]

Maybe there are performance implications? @penghuo could you clarify if and why this limitation is important to the users?