Expanded instruments to include all GFZ indices

[aburrell]

Description

Addresses #90 by adding the new GFZ Hpo and apo indices. Added a general download function for GFZ data and expanded the existing F10.7 and SSN instruments to include the GFZ data as options.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

import pysat
import pysatSpaceWeather as py_sw
import datetime as dt

hpo = pysat.Instrument(inst_module=py_sw.instruments.sw_hpo, tag='now', inst_id='30min')
stime = dt.datetime(2014, 3, 26)
hpo.download(start=stime)
hpo.load(date=stime)
hpo.data[:10]

Yields

2014-03-26 00:00:00  3.667
2014-03-26 00:30:00  4.667
2014-03-26 01:00:00  3.333
2014-03-26 01:30:00  3.333
2014-03-26 02:00:00  3.000
2014-03-26 02:30:00  2.667
2014-03-26 03:00:00  1.667
2014-03-26 03:30:00  1.333
2014-03-26 04:00:00  1.333
2014-03-26 04:30:00  1.667

Currently the apo downloads don't work because the query at GFZ is broken. I contacted them and hopefully it will be fixed soon. apo downloads have been fixed, GFZ responded very quickly.

Test Configuration

• Operating system: OS X Big Sur
• Version number: Python 3.9
• Any details about your local setup that are relevant: develop branch of pysat

Checklist:

• [x] Make sure you are merging into the develop (not main) branch
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] Add a note to CHANGELOG.md, summarizing the changes

If this is a release PR, replace the first item of the above checklist with the release checklist on the pysat wiki: https://github.com/pysat/pysat/wiki/Checklist-for-Release