Add UI option for omitting field label

[cowbellerina]

Reasons for making this change

Sometimes you may want to render fields without label associated with them.

While it's possible to control the rendering of the field by creating a custom field template, or by hiding the label using CSS, they both feel non-ideal for basic use cases where you simply want to get rid of the label.

This PR introduces a new label option within ui:options. Setting the label to false will omit the label. The option won't have any effect on fields where the label is omitted already, even if it's set to true.

const schema = {type: "string"};
const uiSchema = {
  "ui:options": {
    label: false
  }
};

I'm not sure if ui:options -> label is the best place put this under. Instead of ui:showLabel or ui:hideLabel I went with this solution to potentially support other than boolean values. For example, some label value could support rendering the label for screenreaders only.

After making the change, I noticed this subject has been discussed before in #51

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
  • If I'm adding a new section, I've updated the Table of Content
• I'm adding or updating code
  • I've added and/or updated tests
  • I've updated docs if needed
  • I've run npm run cs-format on my branch to conform my code to prettier coding style
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[n1k0]

LGTM with a pending question though.

[n1k0]

I'm surprised this works without a default value set to true; hint?

[cowbellerina]

Yeah, it did work because the default value is set in DefaultTemplate.defaultProps.

Anyways, it's clearer for the reader if the default value is also set here. I made the necessary changes to the code.

[n1k0]

Thank you 👍

[n1k0]

Released in v0.47.0.