Adding default provider and options provider pattern for platform users

[djpugh]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• [*] Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Have you updated the appropriate files

Please check that you have (if appropriate):

• [*] Updated the documentation
• Updated README.md
• [*] Executed pre-commit run --all-files with no errors
• [*] The change is fully covered by automated unit tests

What is the new behavior?

Optional default_provider and options_provider pattern (for platform users) to fetch runtime variables/settings

[sonarqubecloud]

Quality Gate passed

Issues
9 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

☂️ Code Coverage

current status: ✅

Overall Coverage

Statements	Covered	Coverage	Threshold	Status
4174	3692	88%	80%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
src/nskit/client/field_models.py	100%	🟢
src/nskit/client/field_parser.py	96%	🟢
src/nskit/client/interactive.py	89%	🟢
src/nskit/mixer/components/recipe.py	92%	🟢
TOTAL	94%	🟢

updated for commit: 99e4f86 by action🐍