Create two functions to add startDate and endDate

[YetAnotherJonWilson]

Determine if this function will automatically add the predicate ldp:Contains to our periodTracker container. If not, we might need to figure out how to do that first, and create an issue for it.

How to do this with solid-client should be found here: https://docs.inrupt.com/developer-tools/javascript/client-libraries/tutorial/read-write-data/

Currently, I'm thinking we can just create an array of objects like this: [{schema.org/startDate: [Date], schema.org/endDate: [Date]}, {...}, {...}]

We'll probably want to add more data later, here's one resource that discusses different data to track and why, and also lists some apps and briefly compares the data they track: https://www.allaboutwomenmd.com/knowledge-center/tracking-your-period.html

One possible issue related to RDF data: 1) the schema.org startDate and endDate data types have a list titled "Used on these types", with entries like "Event" or "Schedule"--do we need to use these?