feat: Adding support for logging case configuration

[t1agob]

closes #92.

Description of changes:

Adding support for logging case configuration. The default across runtimes in Snake case which allows developers to search across different services independent of which runtime they are using.

• Adding support for new environment variable POWERTOOLS_LOGGER_CASE that overrides default log output case.
• Adding support for changing the log output casing based on environment variable
• Adding supporting documentation for this new feature
• Updated existing documentation cloudwatch logs examples to snake case
• Adding unit tests to validate this new feature

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)

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