ENH - Design system implementation

[trallard]

Now that the design system has been completed, we are ready to move on to an implementation phase (see #265).

There are several tasks needed for this.

### Design
- [ ] https://github.com/conda-incubator/conda-store-ui/issues/344
- [ ] Add contribution details/instructions

### Development
- [ ] https://github.com/conda-incubator/conda-store-ui/issues/291
- [x] Add global color variables - https://github.com/conda-incubator/conda-store-ui/pull/292
- [x] Implement button components - https://github.com/conda-incubator/conda-store-ui/pull/304
- [x] Implement input components - https://github.com/conda-incubator/conda-store-ui/pull/313
- [x] Implement links components - https://github.com/conda-incubator/conda-store-ui/pull/320
- [x] Implement compliant icons with the design system
- [x] Check that only the global color variables are used across all the code base

This is separate from any other workflow-related improvements needed throughout the project.

🛠 Since this implementation is a significant amount of work, we will proceed as follows:

1. Create a design-system-implementation branch and open a PR against main that will close #288 (this issue). This should be marked as draft and visibly signalled as WIP.
2. Follow an iterative development approach by opening multiple small, well-scoped, easy-to-review PRs against the design-system-implementation branch
3. Once completed and validated, then we can merge design-system-implementation into main

[smeragoel]

The design system documentation is in draft here: https://hackmd.io/@S1meqA60T5ycyQ3qIxy4GA/condadesignsystem I'll solicit formal feedback when this I am done with the first version of the draft! 😺

[kcpevey]

@steff456 will update the checkboxes above to link to open PRs. Then meet with @smeragoel to discuss next steps.

[costrouc]

This is a meta issue and all the progress is in the smaller sub-issues.