feat: add modified date timestamps to artifacts

[gasperzgonec]

Description

This change adds timestamps (number of ms since EPOCH) to artifacts, to improve debuggability and improve the reporting by adding user-readable time information of last extraction.

Before

      {
        id: 'artifact-1780473180514-6y1t76ilf',
        item_type: 'todos',
        item_count: 15
      },

New

      {
        id: 'artifact-1780476433181-f5fvke1ps',
        item_type: 'todos',
        item_count: 15,
        oldest_created_date: 1527840000000,
        newest_created_date: 1768035600000,
        oldest_modified_date: 1527840000000,
        newest_modified_date: 1772359200000
      },

Connected Issues

• #ASCPT-22

Checklist

• Tests added/updated and ran with npm run test OR no tests needed.
• Ran backwards compatibility tests with npm run test:backwards-compatibility.
• Code formatted and checked with npm run lint.
• Tested airdrop-template linked to this PR.
• Documentation updated and provided a link to PR / new docs OR no docs needed.

[radovanjorgic]

Closing because we opened new PR which merges #202 and #205