feat(recommend): add client

[shortcuts]

Q	A
Bug fix?	yes
New feature?	yes
BC breaks?	no
Related Issue	Fixes #537
Need Doc update	yes

Describe your change

This PR introduces the Recommend client with the following methods:

• get_recommendations
• get_related_products
• get_frequently_bought_together

[DevinCodes]

Instead of testing that the _transporter.retry gets called with the right parameters, do you think it would it be possible to test the actual request being created? This would allow us to reuse the request definitions for the common test suite we're working towards.

You can see the requests that need to be made in this PR for the Ruby client.

[shortcuts]

do you think it would it be possible to test the actual request being created?

@DevinCodes I don't know Python enough to affirm it is. After the step I've tested, the hosts gets randomly assigned and the payload translated to a Request object before being sent. I feel like the assertion is close enough to the CTS but let me know if I should dig your suggestion.

[DevinCodes]

@shortcuts I think you should be able to mock the requester (as you do the transporter rn), and then assert that the request object it gets passed contains the right values (method, path, body,...). I'm not entirely sure though, since I don't know enough Python as well 😅 Perhaps @tkrugg could point in the right direction here?

[shortcuts]

last check before mergning? @tkrugg @DevinCodes :D

[DevinCodes]

This looks great, thank you @shortcuts !