docs: Document HTTP request parameters for downsampler and influxdb_to_iceberg plugins

[jstirnaman]

Summary

The downsampler and influxdb_to_iceberg plugins support both scheduled and http trigger types, but their HTTP request parameters are not formally documented in the plugin metadata or README files.

Current State

• Both plugins have scheduled_args_config in their docstrings
• Neither has http_args_config for HTTP-specific parameters
• HTTP handlers accept parameters via request body that differ from scheduled trigger arguments

downsampler

HTTP mode uses different/additional parameters:

• backfill_start, backfill_end instead of window
• batch_size for chunked processing
• tag_values as JSON object instead of string format

influxdb_to_iceberg

Likely similar situation — needs code review to identify HTTP-specific parameters.

Recommended Actions

1. Review process_request functions in both plugins to identify all HTTP parameters
2. Add http_args_config to plugin docstrings for Explorer UI support
3. Add ### HTTP request parameters section to READMEs following the pattern in prophet_forecasting

Related

• Prophet forecasting already has separate sections: ### Scheduled trigger parameters and ### HTTP request parameters
• See commit ab1b21f for the pattern to follow