feat: unique invite links for organisations

[Ace2489]

Description

This PR adds the required code for the generation of unique invite links for organisations. These differ from the per-user invite links in that any user can use these links. Also, an organisation can only have one of these.

Changes proposed

What were you told to do?

Generate endpoint and backing code to generate unique invite links for organisations.

What did you do?

• Created an endpoint for client-side access.
• Created the backing methods, commands, and handlers to enable the above.

Check List (Check all the applicable boxes)

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• [x] My code follows the code style of this project.
• [x] This PR does not contain plagiarized content.
• [x] The title and description of the PR is clear and explains the approach.
• [x] I am making a pull request against the dev branch (left side).
• [x] My commit messages styles matches our requested structure.
• [x] My code additions will fail neither code linting checks nor unit test.
• [x] I am only making changes to files I was requested to.

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