[Implement] Create filepicker input component

[vsgoulart]

Design mocks: link

What should we do?

• Create a new filepicker input based on the design mocks
  • This new input will be keyed
  • This new input will have 2 new configuration properties: accept which configures the file extensions the input can select and multiple which configures if the file picker can select multiple files
  • The file values should not be included in the data on the form submit event because files can be too big. Instead we will create a separate file store which costumers users can consume on a case by case basis. The file key will be provided on the submit even data instead of the file values.

Why should we do it?

• Managing documents is a common use case when dealing with forms
• So we can add document handling to the Camunda 8 ecosystem

[Skaiir]

Closed via https://github.com/bpmn-io/form-js/pull/1246