Forbid negative values for "weight" in Function Score Query

[mayya-sharipova]

If a negative weight is submitted for a query:

• issue a deprecation message for 6.x
• error for 7

related to #24910

[elasticmachine]

Pinging @elastic/es-search-aggs

[aditya-agrawal]

Hi, I would like to pick this issue.

[mayya-sharipova]

Thanks @aditya-agrawal, your PR would be very much appreciated

[mayya-sharipova]

@aditya-agrawal We have an urgent need for this PR, as we are preparing for Lucene 8 upgrade. Do you think you will be able to submit a PR within several days?

If not, no problem, we can work on it ourselves.

[aditya-agrawal]

@mayya-sharipova yes I will try to complete this in few days.