Avoid hardcoding file paths in _is_local_manifest_command

[coderabbitai]

In the _is_local_manifest_command function, the path to the manifest.yaml is hardcoded as "/airbyte/integration_code/source_declarative_manifest/manifest.yaml". It would be beneficial to derive this path dynamically or make it configurable to improve portability, especially if the directory structure changes in the future.

Reference:

• PR: Feat: Incorporate SDM in CDK and add publish workflow #58
• Comment: Feat: Incorporate SDM in CDK and add publish workflow #58 (comment)

Requested by: Aaron ("AJ") Steers (@aaronsteers)