Add missing prettier plugin for import ordering

[spalladino]

#1069 added enforcement for import orders, but it depends on a prettier plugin that was not included, so all formatting runs failed to format imports with the warnings:

[warn] Ignored unknown option { importOrder: ["^@aztec/(.*)$", "<THIRD_PARTY_MODULES>", "^\\./|\\.\\./"] }.
[warn] Ignored unknown option { importOrderSeparation: true }.
[warn] Ignored unknown option { importOrderSortSpecifiers: true }.

This PR adds the missing plugin as a dependency, re-formats all files, and adds a setting to handle the type: json type assertion in imports (which failed with an error otherwise).

[spypsy]

ah, apologies I may have had it installed globally