feat: add optional charset option to multipart body parser

[salesh]

Related to #932

This seemed like something I could contribute to, please let me know if I missed anything

[salesh]

this test was completely wrong, I am trying to figure out more correct example - any help would be appreciated

[willfarrell]

Thanks for the PR. A test when binary is passed in will be needed. See the v2 branch when binary was the default for a test that can be copied in. https://github.com/middyjs/middy/blob/2.x/packages/http-multipart-body-parser/__tests__/index.js

[salesh]

Thanks for the PR. A test when binary is passed in will be needed. See the v2 branch when binary was the default for a test that can be copied in. https://github.com/middyjs/middy/blob/2.x/packages/http-multipart-body-parser/__tests__/index.js

That test has an issue

  It should parse an array from a multipart/form-data request (binary)

  Rejected promise returned by test. Reason:

  UnprocessableEntityError (HttpError) {
    expose: true,
    status: 422,
    statusCode: 422,
    message: 'Invalid or malformed multipart/form-data was provided',
  }

how I understand it - an empty body is the root of the issue for that one