docs(idempotency): add support for DynamoDB composite keys

[to-mc]

Issue #, if available: #694

Description of changes:

Update documentation to reflect new feature supporting composite primary keys for DynamoDB in idempotency utility.

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.

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View rendered docs/utilities/idempotency.md

[codecov-commenter]

Codecov Report

Merging #808 (c30ed7c) into develop (6c451f7) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #808   +/-   ##
========================================
  Coverage    99.90%   99.90%           
========================================
  Files          118      118           
  Lines         5078     5107   +29     
  Branches       279      279           
========================================
+ Hits          5073     5102   +29     
  Misses           2        2           
  Partials         3        3           

Impacted Files	Coverage Δ
aws_lambda_powertools/logging/logger.py	100.00% <0.00%> (ø)
aws_lambda_powertools/tracing/tracer.py	100.00% <0.00%> (ø)
aws_lambda_powertools/metrics/metrics.py	100.00% <0.00%> (ø)
aws_lambda_powertools/logging/formatter.py	100.00% <0.00%> (ø)
aws_lambda_powertools/utilities/batch/base.py	100.00% <0.00%> (ø)
...ws_lambda_powertools/middleware_factory/factory.py	100.00% <0.00%> (ø)
...s_lambda_powertools/utilities/parser/models/sns.py	100.00% <0.00%> (ø)
..._lambda_powertools/utilities/feature_flags/base.py	100.00% <0.00%> (ø)
...lambda_powertools/utilities/parser/models/apigw.py	100.00% <0.00%> (ø)
...ambda_powertools/utilities/feature_flags/schema.py	100.00% <0.00%> (ø)
... and 5 more

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[heitorlessa]

Great addition!!!