docs: Minor correction of Lambda name in README

[techeditor]

Issue #

A minor correction of Lambda name in READMEs to get alignment with the actual deployment result.
A Lambda function name is {StackName}-{LogicalId}-{RandomString} by default if the property FunctionName is not defined.

• The code changes have been fully tested
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of the least privilege, etc.)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

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