fix: Upgrade mypy version to build with Python3.8

[sewardgw]

Signed-off-by: Grant Seward grant@stemma.ai

This PR addresses issue: amundsen-io/amundsen#974

Summary of Changes

This PR updates the version of mypy in order to make amundsenfrontend compatible with Python3.8. The prior version of mypy had a bug that prevented it from being installed in Python3.8 but this bug was resolved in 2019. The version was bumped to the newest mypy version (.812), simply because the other Amundsen services were not already aligned on a specific version but I can see that it would also make sense to match the metadata service version (.782). I'll look for feedback here.

There are no material impacts to the code as part of this PR and the majority of the changes are to add explicit typing to several tests. However, the newer version of mypy requires more explicit typing in a few places and therefore there have been a few places where the formatting of the code has been updated. An example of this is that the new mypy infers all dict.get(...) methods to be Optional an in order to meet function signatures changes were made from:

my_dict.get('val')

to

my_dict['val']

The scenarios where these occur are only where the dictionary is guaranteed to contain the key.

In addition, the signature for the BaseMailClient function send_email was updated to be more inline with the example that implements the base client. Optional data, sender and recipient are all now optional. This also conforms to the existing tests which pass in None for these three arguments.

In a few of the more-complex cases # type: ignore was added.

Tests

No new tests were added but several tests were refactored / consolidated.

Documentation

n/a

CheckList

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[dorianj]

LGTM

Can the github workflow be updated to test on 3.8 as well?

[sewardgw]

Yep - adding it now