add link to create new variant if none

[zachariah-at-msupply]

Fixes Part 1 of #5554

👩🏻‍💻 What does this PR do?

Adds a create new variant link on the catalogue>item>variants tab, if there are no variants present.

💌 Any notes for the reviewer?

The capitalisation seems a bit dodgy. It seems all the 'create a new one' links will be similar. Using a function called toLocaleLowerCase() in the NothingHere.tsx file can solve this - should I create an issue to do that?

🧪 Testing

• log in to your open mSupply central server
• go to cataogue>item page and then click on an item that has no variants to see its detail view
• go to the variants tab
• see if the link that says 'create a new one' functions the same as the 'add variant' button on the top right of the variants tab page.

📃 Documentation

• Part of an epic: documentation will be completed for the feature as a whole
• No documentation required: no user facing changes or a bug fix which isn't a change in behaviour
• These areas should be updated or checked:
  1.
  2.

[github-actions]

Bundle size difference

Comparing this PR to main

Old size	New size	Diff
4.99 MB	4.99 MB	67 B (0.00%)

[zachariah-at-msupply]

I have closed this PR and deleted the branch in order to make a branch for each part of issue 5554, and make PRs for them separately, since this was requested in the discussion of the original issue :)