Web Import: Add New Entries to 'Imported Entries' Group

[paudelritij]

Closes #12548
This PR introduce feature to add new group "Imported Entries"

To Do

• Link preferences configuration to BibEntry (for enable/disable and name of group)
• Configure Meta data for imported entries group
• Introduce Smart Group 1 SmartGroup:Import entries\
• [?] Create library-specific settings for particular imported entries group for name and disable/enable option
• Add test cases

Done

• Add configurable field for Imported entries group in preferences
• Create fields for Import entries group in library preferences

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [.] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• [.] Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• [.] Screenshots added in PR description (if change is visible to the user)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[trag-bot]

The new UI elements 'addImportedEntries' and 'addImportedEntriesGroupName' should have their labels localized using Localization.lang to support multilingual functionality.

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Note that your PR will not be reviewed/accepted until you have gone through the mandatory checks in the description and marked each of them them exactly in the format of [x] (done), [ ] (not done yet) or [/] (not applicable).