Allow GlobalBias to take projection and color palette as arguments

[silviacaprioli]

PR description:

This PR adds the possibility to choose different projections and color palettes in bias maps.
This is particularly useful for SeaIce diagnostic.

Issues closed by this pull request:

Close #1460

People involved:

Tag here relevant people to involve in the discussion:

@tovaz92

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• Diagnostic config files path are updated in the console if needed

[silviacaprioli]

Design question regarding how to pass projection types in global_biases.

• Define the projection as a string in the config file, e.g. ccrs.Orthographic(central_longitude=0, central_latitude=90), and then use eval() to instantiate it, but this feels honestly a bit hacky.

• Create a centralized file with predefined projections and use keywords in the config, which are then mapped to actual cartopy projections.

Option 2 feels cleaner, especially if multiple diagnostics will share this logic. The only tricky part is supporting optional arguments for some projections...

tagging @mnurisso @oloapinivad @jhardenberg for discussion