Support resolution of all data-* attributes of links

[petrsvihlik]

Motivation

The current solution supports the resolution of only data-item-id (in the ContentLinkResolver) and data-asset-id (in the RichTextContentConverter). Other data attributes are unsupported.

The problem is related to #243

Proposed solution

Add support for resolution of:

• data-email-address
• data-email-subject
• data-new-window

Additional context

Sample request: https://deliver.kontent.ai/900564fb-873d-4916-ac65-ae148ef3ae12/items

 "modular_content": [],
          "value": "<p><a data-email-address=\"[email protected]\" data-email-subject=\"hey!\" href=\"mailto:[email protected]?subject=hey%21\">Mail link</a></p>\n<p>texttext</p>\n<p><a href=\"https://kontent.ai/\" data-new-window=\"true\" title=\"this leads to heaven\" target=\"_blank\" rel=\"noopener noreferrer\">Web Link</a>&nbsp;</p>\n<p>someothertext</p>\n<p><a data-asset-id=\"8d6096cf-5617-4e33-ae9d-f3b596ed557c\" href=\"https://assets-us-01.kc-usercontent.com:443/900564fb-873d-4916-ac65-ae148ef3ae12/dfac4580-5434-489a-9a4c-5501a4fff3d3/avocado-icon-24x24.png\">Asset link</a></p>\n<p>extra text</p>\n<p><a data-item-id=\"65de4914-d241-4f1f-8079-511b3461b438\" href=\"\">Content Item link</a></p>\n<p>final text&nbsp;</p>"
        },