Add sagemaker e2e tests for sagemaker extensions

[vpaiu]

Issue

D356351411

Description of Changes

Added the following tests for SageMaker functionality:

• Created test folder for SageMaker extensions tests.
• Added the equivalent of the existing SageMaker e2e test(https://github.com/aws/sagemaker-code-editor/blob/main/test/integ/cypress/specs/added-features/extensions.cy.ts). It tests extensions installation via terminal commands.
• Added test for the SageMaker Idle Extension. Tests that the last-active-timestamp is updated when there is activity.
• Added test for SageMaker UI Dark Theme extensions. Tests that the dark theme is set by default.

Testing

• Ran the tests locally

Screenshots/Videos

N/A

Additional Notes

N/A

Backporting

N/A

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