Genericise data use terms for other maintainers

[theosanderson]

Tasks (though we don't have to tackle them all at once):

• use site name instead of "Pathoplexus" in all UI related to data-use-terms
• incorporate specific open and closed URL routes into routes (or in due course introduce more data use terms than just these two?)
• allow customisation of the UI elements that talk about acknowledging the terms of use. E.g. for open does this involve submission to INSDC for a specific instance? Probably provide free text for these
• allow customisation of pages about the terms of use, whether by specifying their HTML or links to offsite pages
• make a PR on Pathoplexus with any changes needed due to the above
• potentially remove the enforcement of a limited time period on restricted terms (when chosen by maintainers)