add GH action for CD on pull request

[yiwen-h]

closes #153

[yiwen-h]

Have something that works and deploys here
Issues:

if there's more than one PR, the most recent one will overwrite the older one
The URL doesn't automatically appear in the PR in the same nice way that it does in the data_science action; is this important?

[StatsRhian]

The over-writing is not ideal and could be a bit confusing. But I don't know how to recreate the "nice" GHA on DS on here yet.

So yeah let's just go for it?