New variable: {{file_publish_uri}} for Obsidian Publish

[Taitava]

I'd like to create a variable for retrieving the current note file's URI in Obsidian Publish service.

This would need support from Obsidian API: https://forum.obsidian.md/t/get-a-files-obsidian-publish-uri-via-the-api/48307

The variable would only be available if Obsidian Publish core plugin is enabled.

[Taitava]

Note to self: Install this plugin, test it, and write code taking example from this: https://github.com/kometenstaub/copy-publish-url/blob/af1d88dfad00cc6fdd0411482d4ab8a57228e382/src/main.ts#L44-L67
Give credits to the original author.