STY: reduce duplication for init and clean

[jklenzing]

Description

Addresses #89, #118

Adds two general instrument methods which are frequently repeated:

• init, where the initialization routine reads from a standard mission-level module (cnofs, de2, icon)
• clean_warn, a custom clean routine that warns users that cleaning is not available

Additionally, suppresses logger messages during package-level imports of constellation objects. This is required to keep the logger from being saturated until this issue is fixed at the pysat-level. Otherwise verifying the logger here is near-impossible.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

import pysat
import logging
pysat.logger.setLevel(logging.INFO)
ivm = pysat.Instrument('cnofs', 'ivm')

acknowledgement string should go to the logger, and ivm.acknowledgements and ivm.references updated accordingly.

Can be repeated for the cnofs, de2, and icon instruments

For cleaning, attempt to load de2 data, look for the warning.

Test Configuration

• Operating system: Mac OS X Big Sur
• Version number: python 3.8.11
• Any details about your local setup that are relevant

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
• [x] Update zenodo.json file for new code contributors

[jklenzing]

Topics to discuss:

• local changes to constellation objects
• should other instruments conform to the module style and use custom init

[jklenzing]

I've decided this pull is large enough for review. Follow-on work to update other instruments documented in #119, including consistency issues that are out of scope here.