Introduction of configuration option to simplify GADM tolerance

[SermishaNarayana]

Closes # (if applicable).

Changes proposed in this Pull Request

In this PR, a configuration feature has been added that can be used to quantitatively vary the tolerance levels of GADM shapes simplification.

Checklist

• I consent to the release of this PR's code under the AGPLv3 license and non-code contributions under CC0-1.0 and CC-BY-4.0.
• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Newly introduced dependencies are added to envs/environment.yaml and doc/requirements.txt.
• Changes in configuration options are added in all of config.default.yaml and config.tutorial.yaml.
• Add a test config or line additions to test/ (note tests are changing the config.tutorial.yaml)
• Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[davide-f]

Hello @SermishaNarayana :D

The functionality of this PR is great and basically ready to merge; as a summary of last talks, the missing element was to add the minarea option (see argument of _simplify_polys) and then it is ready to go.
Probably it is better to first finalize the sister #1138 PR , to solve conflicts that may arise.

What do you think?

[davide-f]

Hello @SermishaNarayana :D Just pinging to catch on the status of this PR :)