Add/remove projects to/from a folder

[sergii-bond]

What does this PR do?

Implements this feature in SDK and CLI:

Type of Change

• New feature (non-breaking change that adds functionality)

Testing

• I have tested this change locally
• I have added/updated tests for this change

Test details:

% roboflow folder list                                                                              
NAME      ID                    PROJECTS
--------  --------------------  --------
Other     DcudV3C2dWb21lMuMGru  0
rf100-vl  qqsFr7HheczCzclNCmfE  8

% roboflow folder add-projects qqsFr7HheczCzclNCmfE "circuit-voltages-ulq2t"                       
Added 1 project(s) to folder 'qqsFr7HheczCzclNCmfE'

% roboflow folder remove-projects qqsFr7HheczCzclNCmfE "circuit-voltages-ulq2t"               
Removed 1 project(s) from folder 'qqsFr7HheczCzclNCmfE'

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in hard-to-understand areas
• My changes generate no new warnings or errors
• I have updated the documentation accordingly (if applicable)

Additional Context

[tonylampada]

lgtm!