fix(storage-r2): upload with the correct contentType

[rjgtav]

What?

Use the correct Content-Type when uploading files to R2.

Why?

While R2 can infer the Content-Type of most uploads, in some scenarios it will fail (e.g. when uploading an SVG image).

How?

By passing the file's MIME type as the Content-Type header.

Bug report: https://discord.com/channels/967097582721572934/1422639568808841329/1422645245534797914

[github-actions]

Pull Request titles must follow the Conventional Commits specification and have valid scopes.

Unknown scope "storage-r2" found in pull request title "fix(storage-r2): upload with the correct contentType". Scope must match one of: cpa, db-*, db-mongodb, db-postgres, db-vercel-postgres, db-sqlite, drizzle, email-*, email-nodemailer, email-resend, eslint, graphql, live-preview, live-preview-react, next, payload-cloud, plugin-cloud, plugin-cloud-storage, plugin-form-builder, plugin-import-export, plugin-multi-tenant, plugin-nested-docs, plugin-redirects, plugin-search, plugin-sentry, plugin-seo, plugin-stripe, richtext-*, richtext-lexical, richtext-slate, sdk, storage-*, storage-azure, storage-gcs, storage-uploadthing, storage-vercel-blob, storage-s3, translations, ui, templates, examples(/(\w|-)+)?, deps.

feat(ui): add Button component
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