Set a single source of truth for types

[mtruj013]

Done

• Refactored imports so that they come from one place and we don't have to define changes repeatedly throughout the code. Continuation of this discussion

QA

• There is no change to functionality being introduced here, so test should pass as expected

Issue / Card

Fixes https://warthogs.atlassian.net/browse/WD-14516

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.63%. Comparing base (35702b8) to head (aef7928). Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
webapp/schemas.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #177 +/- ## ========================================== + Coverage 87.38% 87.63% +0.24% ========================================== Files 30 37 +7 Lines 1665 1819 +154 ========================================== + Hits 1455 1594 +139 - Misses 210 225 +15 ``` | [Flag](https://app.codecov.io/gh/canonical/ubuntu-com-security-api/pull/177/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=canonical) | Coverage Δ | | |---|---|---| | [python](https://app.codecov.io/gh/canonical/ubuntu-com-security-api/pull/177/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=canonical) | `87.63% <94.11%> (+0.24%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=canonical#carryforward-flags-in-the-pull-request-comment) to find out more.

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