Consolidate and fix workspace resolution

[Pwuts]

Background

Currently, four commands use three different ways to resolve the workspace path and all implement it themselves. Also, workspace path resolution is broken for execute_shell.

PR #1903 also fixes the immediate failure of execute_code.py and image_gen.py, but does not address the unordered approach in other files.

Changes

• Consolidated workspace resolution functionality in autogpt/workspace.py

Documentation

No changes for users, so no docs needed.

Test Plan

Tested by letting Auto-GPT read a file in the workspace, both directly and using cat.

PR Quality Checklist

• My pull request is atomic and focuses on a single change.
• I have thoroughly tested my changes with multiple different prompts.
• I have considered potential risks and mitigations for my changes.
• I have documented my changes clearly and comprehensively.
• I have not snuck in any "extra" small tweaks changes

[hdkiller]

I am not sure if this PR related to your implementation but worth a look.

[Pwuts]

@hdkiller I think that vulnerability should be fixed here. :)