feat: add docs for GoTrue (Sourcery refactored)

[sourcery-ai]

Pull Request #180 refactored by Sourcery.

If you're happy with these changes, merge this Pull Request using the Squash and merge strategy.

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[sourcery-ai]

Function AsyncGoTrueAPI._create_request_headers refactored with the following changes:

• Merge dictionary assignment with declaration (merge-dict-assign)

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.13%.

Quality metrics	Before	After	Change
Complexity	0.79 ⭐	0.80 ⭐	0.01 👎
Method Length	53.27 ⭐	53.15 ⭐	-0.12 👍
Working memory	6.76 🙂	6.80 🙂	0.04 👎
Quality	80.72% ⭐	80.59% ⭐	-0.13% 👎

Other metrics	Before	After	Change
Lines	615	614	-1

Changed files	Quality Before	Quality After	Quality Change
gotrue/_async/api.py	80.72% ⭐	80.59% ⭐	-0.13% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation

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