Rename Field View prop from isReadOnly to isDisabled

[gautamsi]

ref #2258

It makes more sense to have Field View to use isDisabled prop rather than isReadOnly

this PR:

• renames prop for Field Views (only) to isDisabled from isReadOnly
  • Does not change the api for public, it remains adminConfig: { isReadOnly: true }
• fixes disable issue in wysiwyg field.
• added test for wysiwyg field being read only.

I have not added changeset as this should be merged to #2258 for release.
updated changeset for #2258 to reflect the change.

[changeset-bot]

💥 No Changeset

Latest commit: 937aed6

Merging this PR will not cause any packages to be released. If these changes should not cause updates to packages in this repo, this is fine 🙂

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This PR includes changesets to release 6 packages

Name	Type
@keystonejs/app-admin-ui	Minor
@keystonejs/field-content	Minor
@keystonejs/fields-markdown	Minor
@keystonejs/fields-wysiwyg-tinymce	Minor
@keystonejs/fields	Minor
@keystonejs/cypress-project-access-control	Patch

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[timleslie]

Yep, I think this is a good change 👍