Add checks for existing Lambda function in workflow - #14

Unexpected input(s) 'env-vars', valid inputs are ['function-name', 'code-artifacts-dir', 'handler', 'runtime', 's3-bucket', 's3-key', 'publish', 'dry-run', 'revision-id', 'architectures', 'source-kms-key-arn', 'role', 'function-description', 'memory-size', 'timeout', 'vpc-config', 'environment', 'dead-letter-config', 'kms-key-arn', 'tracing-config', 'layers', 'file-system-configs', 'image-config', 'ephemeral-storage', 'snap-start', 'logging-config', 'code-signing-config-arn', 'tags']