[sitecore-jss] [sitecore-jss-angular] Field metadata chromes in editMode metadata

[stasmaxymov]

• [x] This PR follows the Contribution Guide
• [x] Changelog updated
• [ ] Upgrade guide entry added

Description / Motivation

This PR enables editing support for the fields in editing mode for editMode metadata. When a field is rendered in metadata mode it will be surrounded with open and close code elements with metadata content. This elements indicate location of the field and provide required metadata to enable editing in editor applications like Pages. The fields with this functionality are:

[sitecore-jss-angular] image.directive.ts [sitecore-jss-angular] date.directive.ts [sitecore-jss-angular] rich-text.directive.ts [sitecore-jss-angular] text.directive.ts [sitecore-jss-angular] link.directive.ts [sitecore-jss-angular] router-link.directive.ts [sitecore-jss-angular] generic-link.directive.spec.ts

Testing Details

• [x] Unit Test Added
• [ ] Manual Test/Other (Please elaborate)

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)