Option to set gunicorn --limit-request-line from common_site_config.json

Issue: Feature Request

**Is your feature request related to a problem? Please describe.**
Sometimes default value of gunicorn `--limit-request-line` (which is 4094) is not enough. I have encountered `Bad Request : Request Line is too large (6010 > 4094)` several times, and mostly when select doctype in Data Export page on ERPNext (ver 11).

**Describe the solution you'd like**
In `supervisor.conf`, add `--limit-request-line` option to gunicorn command, and add config getter in `generate_supervisor_config` function so it could get the config from `common_site_config.json` file.

**Additional context**


Start by locating supervisor.conf and the generate_supervisor_config function, then trace how common_site_config.json values are read into the generated Gunicorn command. Confirm the existing configuration path and make the requested limit-request-line setting appear in the generated command when configured. Done means a common_site_config.json value controls Gunicorn's request-line limit without breaking supervisor configuration.

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