Bind original request to onFile function this

[digitalmio]

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

Gives access to original request via this on onFile function. This should be useful to link file handler with original request or create unique IDs based on request id.
Fixes #427

[digitalmio]

Not sure if I should change package.json too and bump version to 7.5.1?

[Eomm]

Not sure if I should change package.json too and bump version to 7.5.1?

Nope

[digitalmio]

Any chance to get this approved and merged pls?

[liudichen]

what if onFile is an arrow function. this may not be able to point correctly.

[Eomm]

when the user sets the arrow function, it should know that the this context is the upper scope - as it works in the fastify's handler, decorators and hooks