DEV - Update dev workflows and CI

[trallard]

Split from #792

Description

• Remove OS-specific environment.yaml files as no longer needed
• Update env files - server
• Update environment file - core
• Add note about updating dependencies
• Update CI - remove unnecessary yaml files

Pull request checklist

• [x] Did you test this change locally?
• [x] Did you update the documentation (if required)?
• [ ] Did you add/update relevant tests for this change (if required)?

Additional information

With this PR, at most, contributors/maintainers will need to regenerate/update their local conda environment.

How to test

💻 Locally:

1. Regenerate your local conda development environment (should use conda-store-server/environment-dev.yaml
2. Perform your usual development tasks such as running tests, building conda-store, etc.

To test the changes to the test GH workflows, you can use https://github.com/nektos/act and run the workflow or job accordingly. For example, to only run the conda-store integration tests: act -j "integration-test-conda-store-server"

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