fix(parser): mypy support for payload type override as models

[heitorlessa]

Issue #, if available: #857

Description of changes:

This PR allows MyPy to not trigger an error when overriding payload types in built-in models provided by Parser, as described: https://awslabs.github.io/aws-lambda-powertools-python/latest/utilities/parser/#extending-built-in-models

Scenario: There are cases where you want to provide your own Model while retaining access to metadata information about the event. Previously, when using MyPy, this would cause a type override error since payload fields would only support what's expected, not a custom model as docs suggest for non-MyPy customers.

from aws_lambda_powertools.utilities.parser import parse, BaseModel
from aws_lambda_powertools.utilities.parser.models import EventBridgeModel

from typing import List, Optional


class OrderItem(BaseModel):
    id: int
    quantity: int
    description: str


class Order(BaseModel):
    id: int
    description: str
    items: List[OrderItem]


class OrderEventModel(EventBridgeModel):
    detail: Order

Checklist

• Meet tenets criteria
• Update tests
• Update docs
• PR title follows conventional commit semantics

Breaking change checklist

RFC issue #:

• Migration process documented
• Implement warnings (if it can live side by side)

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

Merging #883 (adf324d) into develop (4994349) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #883   +/-   ##
========================================
  Coverage    99.88%   99.88%           
========================================
  Files          118      118           
  Lines         5129     5133    +4     
  Branches       573      573           
========================================
+ Hits          5123     5127    +4     
  Misses           2        2           
  Partials         4        4           

Impacted Files	Coverage Δ
...s_lambda_powertools/utilities/parser/models/alb.py	100.00% <100.00%> (ø)
...lambda_powertools/utilities/parser/models/apigw.py	100.00% <100.00%> (ø)
...mbda_powertools/utilities/parser/models/apigwv2.py	100.00% <100.00%> (ø)
...a_powertools/utilities/parser/models/cloudwatch.py	100.00% <100.00%> (ø)
...bda_powertools/utilities/parser/models/dynamodb.py	100.00% <100.00%> (ø)
...powertools/utilities/parser/models/event_bridge.py	100.00% <100.00%> (ø)
...mbda_powertools/utilities/parser/models/kinesis.py	100.00% <100.00%> (ø)
...ws_lambda_powertools/utilities/parser/models/s3.py	100.00% <100.00%> (ø)
...ertools/utilities/parser/models/s3_object_event.py	100.00% <100.00%> (ø)
...s_lambda_powertools/utilities/parser/models/sns.py	100.00% <100.00%> (ø)
... and 1 more

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