Fix templates to be valid python format strings

[t3chguy]

Subset of #375

Pull Request Checklist

• Pull request includes a changelog file. The entry should:
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[clokep]

Should this have been a bugfix?

[t3chguy]

I presumed the files were to be treated as sample templates rather than the canonical ones, so didn't consider a broken example to be a "bug"

[clokep]

Ah, fair. I'm not sure if we're really clear at how one is to deploy sydent since... it isn't widely deployed beyond us. Carry on! 👍

[richvdh]

it isn't widely deployed beyond us

For what it's worth, I think this is increasingly untrue - despite the fact that the deployment process is undocumented and fraught with footguns (#131 is particularly relevant here)