[Cosmos] deprecate offer-named methods in favor of new throughput-named methods

[simorenoh]

With these changes, we can officially mark read_offer() for deprecation and instantiate the more relevantly named read_throughput() method for database and container levels.

I went ahead and created a new ThroughputProperties object to replace the previously existing Offer object as well to match with the .NET and Java SDKs, although this bit is completely extra and could be reverted if we feel it's not neccessary.

I also know that the reasoning for this was the current state of documentation (which mostly references throughput as opposed to offers) but I found this too: https://docs.microsoft.com/en-us/rest/api/cosmos-db/offers - not sure if this is all there is, but wanted to double check on this point.

[check-enforcer]

This pull request is protected by Check Enforcer.

What is Check Enforcer?

Check Enforcer helps ensure all pull requests are covered by at least one check-run (typically an Azure Pipeline). When all check-runs associated with this pull request pass then Check Enforcer itself will pass.

Why am I getting this message?

You are getting this message because Check Enforcer did not detect any check-runs being associated with this pull request within five minutes. This may indicate that your pull request is not covered by any pipelines and so Check Enforcer is correctly blocking the pull request being merged.

What should I do now?

If the check-enforcer check-run is not passing and all other check-runs associated with this PR are passing (excluding license-cla) then you could try telling Check Enforcer to evaluate your pull request again. You can do this by adding a comment to this pull request as follows:
/check-enforcer evaluate
Typically evaulation only takes a few seconds. If you know that your pull request is not covered by a pipeline and this is expected you can override Check Enforcer using the following command:
/check-enforcer override
Note that using the override command triggers alerts so that follow-up investigations can occur (PRs still need to be approved as normal).

What if I am onboarding a new service?

Often, new services do not have validation pipelines associated with them, in order to bootstrap pipelines for a new service, you can issue the following command as a pull request comment:
/azp run prepare-pipelines
This will run a pipeline that analyzes the source tree and creates the pipelines necessary to build and validate your pull request. Once the pipeline has been created you can trigger the pipeline using the following comment:
/azp run python - [service] - ci

[tjprescott]

It seems the non-standard indenting is still showing in the diff.

[tjprescott]

So we still have a breaking change on account of wholesale renaming Offer to ThroughputProperties. @annatisch how do you recommend resolving that? Alias Offer to ThroughputProperties?

[annatisch]

Yeah as @tjprescott mentioned - anyone who's written the following code should remain unbroken:

from azure.cosmos.offer import Offer
o = client.read_offer()
if isinstance(o, Offer):
    print(o.properties)

I'm pretty sure for the model itself this could just be aliased. However you'll probably need to keep the offer.py file around.

We're fortunate that this is a response type only (I can't see anywhere a customer would have constructed this themselves), so hopefully the number of people using this directly should be low.

[annatisch]

Looks good - probably just needs a changelog entry?

changes made