Move options to chainladder/_config

[genedan]

Description

chainladder.__init__.py is responsible for several things:

1. Defining the public API
2. Deprecation
3. Options

We should keep the scope of __init__.py to have a single responsibility, that is, the public API. With the options expected to grow in the near future (see #875), we should move these outside of __init__.py.

Is your feature request aligned with the scope of the package?

• Yes, absolutely!
• No, but it's still worth discussing.
• N/A (this request is not a codebase enhancement).

Describe the solution you'd like, or your current workaround.

We should move all code concerning options to a new folder chainladder/_conf.

Do you have any additional supporting notes?

• The public API of the existing features remains unchanged.
• ARCHITECTURE.md must be updated to reflect the change.

Would you be willing to contribute this ticket?

• Yes, absolutely!
• Yes, but I would like some help.
• No.