[Docs] Add docs regarding `filesystem` and `global` environments

[viniciusdc]

The environment names for filesystem and default leads to some misconception about what these environments are used for and how they can be managed. We need to create some documentation around what they are, how they’re used, and what they mean.

[trallard]

TODO:

• [x] renaming of filesystem default
• [ ] update docs as needed

[viniciusdc]

This is blocked until we get the new environments changed in the code-base

[viniciusdc]

We found a bug within conda-store that was blocking the proposed changes. https://github.com/Quansight/qhub/pull/1357 recently fixed it.

This issue is now blocked until the latest version of conda-store is integrated on Nebari.

[pavithraes]

Closing as a duplicate of https://github.com/nebari-dev/nebari-docs/issues/80