Support submissions with date ranges

[emmahodcroft]

Now that we're well on the way to supporting date ranges within Loculus, we should enable users to explicitly upload date ranges.

For example at the moment a date of 1980 will be converted to 1980-01-01 to 1980-12-31 and the date 2014-07 will be converted to 2014-07-01 to 2014-07-31.

However, in some cases people may know more specific date ranges, for example 1982-04 to 1982-07 or 2022-11-10 to 2022-11-15 and we should enable this too!

There are a couple of ways we could support this, but there's an existing ISO standard to use / for dates to indicate ranges, which is also supported by Genbank - so supporting this would kill two birds with one stone.

We could also consider supporting users in uploading two columsn (minDate maxDate) but this would mean more changes to our suggested files & probably more edits on the backend to convert them into our own date format.