Add optional Sentry support for error reporting

CHANGELOG.md

api/auth.go

api/custom/datastores.go

api/custom/exports.go

api/custom/federation.go

api/custom/imports.go

api/custom/media_attributes.go

api/custom/purge.go

api/custom/quarantine.go

api/custom/tasks.go

api/custom/usage.go

api/r0/download.go

api/r0/identicon.go

api/r0/logout.go

api/r0/preview_url.go

api/r0/thumbnail.go

api/r0/upload.go

api/unstable/blurhash_get.go

api/unstable/blurhash_render.go

api/unstable/info.go