Discuss the import function of existing data

## Is your feature request related to a problem? Please describe

There is a requirement related to importing existing data, and we hope you can discuss ideas and implementation approaches.

## Describe the solution you'd like

This is not a core function, so it can be considered as a plugin, and the following points need to be considered:

- Default include a unified import template, allowing users to create import content based on the template
- It is also possible to select data from different platforms and import it accordingly
- Whether the import process involves the import of tags, users, votes, and accepted answers
- Whether the import process should download remote images in the main text

Some import-related issues: #146 #358

The request names no files, tests, or entry points; begin by reading related issues #146 and #358 alongside the import requirements listed here. Done would require an agreed plugin and import scope covering the template, source platforms, tags, users, votes, accepted answers, and remote images.

Written by the indexing model from the issue text.