replace "endpoint_url" parameter in PurviewCollectionsClient class for "account_name" parameter

[edobrynin-dodo]

We use "account_name" parameter in core.PurviewClient class, because it's enough to build endpoint_url from it.
This PR applies the same logic to PurviewCollectionsClient class: you only need to pass account_name, and the endpoint url will be created inside the related functions

[wjohnson]

Hi, @edobrynin-dodo thank you for your interest in PyApacheAtlas and willingness to contribute to the project!

Unfortunately, this might not work as well for all users as there are some cases where we need to construct the endpoint url in advance (due to some internal naming conventions at Microsoft for our testing / internal versions of Purview).

However, I agree, this could be simplified. I would gladly accept a solution that keeps it simple but limits the areas that would have to change the url if a user was specifying a different domain / sub-domain beyond the account name.