Add pagination to list api

[dkuntze]

Description

Add support for the continuation-token method of loading more items from the /list api.

Related Issue

#238 & #150

Motivation and Context

Incremental support for customers that have very large directories full of documents/folders.

How Has This Been Tested?

These api changes should function exactly as it does today. To benefit from these changes, a series of front end changes will need to be made.

Created these tests:

• test/utils/daCtx.test.js: “Continuation token” describe block with 2 tests (query param parsing + default null).
• test/storage/object/list.test.js: “passes continuation token and returns next token”.
• test/index.test.js: “should expose continuation token header for list responses”.

Screenshots (if appropriate):

Types of changes

• 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 change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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