feat: add 'copy original link to this post' menu item

[peterbud]

Description

This PR adds a new context menu item 'Copy original link to post'. Selecting this menu will copy the original URL to the clipboard, aka without the elk.zone prefix

Fixes #1064

Additional context

See #1064

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Translations update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide related snapshots or videos.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).

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