test: add file command test cases

[ermineJose]

Description

Add more command specific testcases for file upload, cost, download commands of autonomi client CLI.

Related Issue

Fixes #<issue_number> (if applicable).

Type of Change

Please mark the types of changes made in this pull request.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Checklist

Please ensure all of the following tasks have been completed:

• I have read the contributing guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have updated the documentation accordingly.
• I have followed the conventional commits guidelines for commit messages.
• I have verified my commit messages with commitlint.