chore: fix ContentType usage

[karolsojko]

Origin

Noticed that there were errors on the server side coming from the @standardnotes/features package caused by the content type comparisons. So I decided to replace the old ContentType usage with new one on the app

What this PR does

• Changes all function parameter declarations of param: ContentType to param: string as the old ContentType was essentially just a string alias. It did not safe-guard the content type on runtime - just a dev env helper.
• Changes invocations of those functions from f.e. ContentType.File to ContentType.TYPES.File

What this PR does not

• it does not replace the parameters with proper ContentType types because that requires more implementation logic and should be done in consecutive PRs. More details below.

How to use ContenType

ContentType is a proper domain value object now which safe-guards its definition during runtime. Here is how to use it:

import { ContentType } from '@standardnotes/domain-core'

// as a function param - this ensures the parameter is a valid content type
function foobar(contentType: ContentType) {
  console.log(contentType.value)
}

// constructing the value object
const contentTypeString = '...'

const contentTypeOrError = ContentType.create(contentTypeString)
if (contentTypeOrError.isFailed()) {
  // the string passed to the value object had an invalid content type that is not allowed
}
const contentType = contentTypeOrError.getValue()
foobar(contentType)

// constructing from predefined strings
const contentType = ContentType.create(ContentType.TYPES.File).getValue()
foobar(contentType)