feat(FR-84): add multiple file download support in folder explorer

[nowgnuesLee]

This PR resolves #2100

changes

• Add a download button between delete and create
• Add _downloadMultipleFiles function on backend-ai-folder-explorer.ts. This function asynchronously requests download link for files to server, with a download interval of 500ms between each files. (If it's too much, it should be taken into consideration.)

Checklist: (if applicable)

• Mention to the original issue
• Documentation
• Minium required manager version
• Specific setting for review (eg., KB link, endpoint or how to setup)
• Minimum requirements to check during review
• Test case(s) to demonstrate the difference of before/after

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[github-actions]

Coverage report for ./react

St.❔	Category	Percentage	Covered / Total
🔴	Statements	4.98% (-0% 🔻)	398/7994
🔴	Branches	4.3% (-0% 🔻)	237/5506
🔴	Functions	2.98% (-0% 🔻)	78/2615
🔴	Lines	4.9% (-0% 🔻)	383/7821

Test suite run success

124 tests passing in 14 suites.

Report generated by 🧪jest coverage report action from fd4012e

[yomybaby]

Let's consider implementing an API for downloading multiple files, including folders.