Enhanced support in weather-dl for downloading data across month ranges spanning multiple years.

I have a suggestion for an enhancement to the `weather-dl` tool. Currently, when downloading data for a `month range` that spans multiple years, the process requires manual splitting of the `month range` into separate configurations and executing multiple jobs for each part. This process can be tedious and time-consuming.

For instance, if we wish to download data from `April 1994` to `August 2012`, and the `target path` follows this format: `(gs://xyz/{year}/{year}{month:02d}_hres_var.grb2)`, we need to split the dates into three parts as follows:

1st part :
`year=1994`
`month=04/to/12`
`day=all`

For the 2nd part:
`year=1995/to/2011`
`month=01/to/12`
`day=all`

And for the last part:
`year=2012`
`month=01/to/08`
`day=all`

I propose an enhancement in the `weather-dl parser` by introducing a new keyword, such as `month_year`, in the configuration.
The value of this keyword would look like `08-2012` or `01-2022`. Additionally, we can add a script to the `parser` of `weather-dl` that can correctly interpret this keyword.

P.S.: A similar use-case can be found in the [Arco-era5 dataset](https://github.com/google-research/arco-era5/blob/main/raw/). Please refer to any file containing `sfc` in the filename for more context.