Add possible ARN value for function_name in aws_lambda_permission resource

[l-teles]

Description

This PR improves the documentation for the aws_lambda_permission resource by specifying that the function ARN is also a possible value for the function_name argument, as seen here for example.

[github-actions]

Welcome @l-teles 👋

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[justinretzolk]

Looks good to me! Thank you for taking the time to raise this! I'll get this merged once the checks finish up.

Resource definition reference

[github-actions]

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