Determine raw data filepath from session and scan info

[yousefmoazzam]

Initially tried to fetch the startTime on InstrumentSession objects with useFragment but was unable to read the data from cache. Feel free to take a look at the following branch where I was only able to read the startTime from the cache using readFragment: https://github.com/DiamondLightSource/ImagingHub/tree/session-year-use-fragment

Pinging @fallars mainly so then you're aware of the incomplete filesystem information for ePSIC, namely:

• I only list the e01 directory in the DLS filesystem, I wasn't sure how to go about tackling the multiple dirs that I see on the DLS filesystem, so I just hardcoded e01 for now
• I didn't fill in a dirname for ePSIC raw data dirs since, while I did see a dir called raw in some e01 visit, I didn't see much in it, so wasn't sure what to put