feat: API for executive calendar references

[ryparker]

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It would be nice to have an API that provides all the executive calendar items that the Senate often references. I can see that Congress.gov already has these indexed based on how it supports searches such as "calendar 511" or URLs such as this

https://www.congress.gov/search?searchResultViewType=compact&q={%22source%22:%22nominations%22,%22search%22:%22calendar+511%22,%22congress%22:%22118%22}

Notice the calendar+511.

This feature would be useful because executive calendar numbers are often referenced in the daily schedule/wrap up on www.democrats.senate.gov, for example. The API data could be used to programmatically identify these referenced items.