[BUG] Handle get key operation when no tag has been set

[PatStLouis]

Handle cases where a key doesn't have a tags property.

@dbluhm @jamshale small but critical bug introduced by my last PR, I was under the impression every key had tags by default but it doesn't seem like so, this will handle such cases.

[PatStLouis]

another fix could be to change this line: https://github.com/OpSecId/aries-cloudagent-python/blob/036f108a5ea4fbc4805b49be6bdc8fd02b1511f6/aries_cloudagent/wallet/askar.py#L100

from:

if kid:
    tags = {"kid": kid}
else:
    tags = None

to

if kid:
    tags = {"kid": kid}
else:
    tags = {}

I believe this would be more consistent as a fix since all keys will have a tags object. Any opinion?

[PatStLouis]

I made a combination of @jamshale suggestion and the latter idea.

[sonarcloud[bot]]

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