Overriding with context manager (one and multiple providers)

[nightblure]

I implement two little features for ease of use during tests:

1. overriding one provider with a context manager. Now you can use it like this:

   
   # old way
   some_provider.override(mock)
   some_provider.reset_override()

new way

with some_provider.override_context(mock): ...

2. overriding multiple providers with a context manager. Now you can use it like this:
```python3
mock_1 = ...
mock2 = ...

# old way
container.provider_1.override(mock_1)
container.provider_2.override(mock_2)
# do something
container.reset_override()

# new way
providers_for_overriding = {
    "provider_1": mock_1,
    "provider_2": mock2,
    # more providers...
}

with container.override_providers(providers_for_overriding):
    # do something

[lesnik512]

@nightblure looks great, thanks!

[nightblure]

we lose coverage on this line after I removed omit. is it acceptable to add # pragma: no cover here?

[lesnik512]

we lose coverage on this line after I removed omit. is it acceptable to add # pragma: no cover here?

yes, it's ok

[nightblure]

thanks for the review! corrected according to your comments, please take a look

[nightblure]

hmm, there is still a question about updating the documentation. I can try to add the relevant sections myself if you allow, or you will do this

[lesnik512]

@nightblure would be great if you'll add docs as well, but it's up to you. Anyway, thank you for your contribution!

[nightblure]

@nightblure would be great if you'll add docs as well, but it's up to you. Anyway, thank you for your contribution!

ok I'll try to do it. within the current MR or separate?

[lesnik512]

@nightblure better in separate, I'll merge this