Use sunpy_soar for downloading data from SOAR

[jgieseler]

sunpy_soar supports since v1.4 also low latency data. So it now is able to obtain all the same data we're downloading until now with solo_epd_loader (the source is in both cases ESA's SOAR). For the future, it would be worthwhile to completely move the downloading process to sunpy_soar to avoid duplication (and sunpy_soar is definitely much better written than my code 😅).

[AthKouloumvakos]

Just some thoughts.

I believe that a list of the functions to change is:

1. _epd_ll_download
2. _epd_l2_download
3. get_available_soar_files
4. _autodownload_cdf

• 1. and 2. can be merged into a new function _epd_download
• 3. can remain and it will return the result of Fido.search. Probably rename this to _epd_search
• 4. This part will be covered by 1. and 2.

Potentially these two functions maybe affected depending how and where the data will be downloaded by sunpy.

1. _get_epd_filelist
2. _get_step_filelist