Move to a conda-only install of pymc

[drbenvincent]

• Related to install pymc in the recommended manner for remote workflows #279
• The recommended install instructions for PyMC is via conda, not pip. We are already doing that, but it seems that at a later step in the setup of the environment that we are basically overwriting that with a pip installed pymc.
• Based on experience with other repo's, it seems that we'll have to:
  • Remove the package dependencies from pyproject.toml and instead place them in environment.yml
  • Build the environment from this new environment.yml
  • Update the instructions in CONTRIBUTING.md
• We shou also re-run the notebooks which show WARNING (pytensor.tensor.blas): Using NumPy C-API based implementation for BLAS functions. because this is indicative of pymc being pip installed rather than conda installed.

• Re-running of diff in diff notebooks is blocked by UFuncTypeError when calling summary method #299. Fix this first.

[drbenvincent]

Note to self: this is being addressed in the some-devops branch