Allow more flexibility in start and end datetimes for az_hourly()

[Aariq]

The following inputs currently error, but it would be cool if they worked in some way:

library(azmetr)
az_hourly(start_date_time = "2023-07-11")
#> Error: `start_date` failed to parse
az_hourly(start_date_time = as.POSIXct("2023-07-11"))
#> Error: `start_date` failed to parse
az_hourly(start_date_time = as.Date("2023-07-11"))
#> Error: `start_date` failed to parse

^{Created on 2023-07-12 with reprex v2.0.2}

If these arguments could accept any level of precision (e.g. by rounding down) then it might be good to deprecate start_date_time and end_date_time (and the equivalents in az_daily()) and replace with just start and end

[Aariq]

Check if vignette can be simplified if and when this change is made

[Aariq]

@jeremylweiss if you could run az_hourly(start = "2023-10-01", end = "2023-10-02") what would you expect to get?

A) 24 readings, one for every hour on the 1st from 01:00:00 to 23:59:59 (ending just before the 2nd)
B) 48 readings going through the end of the 2nd (last data point on 2023-10-02 23:59:59)
C) Something else?

[jeremylweiss]

Friday quiz! I choose 'B'. With the added detail that what comes back has a first data point of 2023-10-01 01:00:00