`SPIDERMON_MONITOR_SKIPPING_RULES` isn't documented

[curita]

SPIDERMON_MONITOR_SKIPPING_RULES (https://github.com/scrapinghub/spidermon/pull/384) doesn't appear to be mentioned in the docs nor the release notes, even though it appears to be available in 1.20.0 (https://github.com/scrapinghub/spidermon/blob/release-1.20.0/spidermon/contrib/scrapy/monitors/base.py#L29C18-L29C50).

The setting is documented in the docstring of BaseScrapyMonitor, but that might not be rendered in the ReadTheDocs pages.