Added option to configure a nonce on the frontend JS script attribute.

[danielmorell]

Description of the change

Adding a nonce attribute for inline frontend JS scripts is important for CSP policy. Previously there was no way to add a nonce attribute to the frontend error monitoring JS script. This resolves that issue by adding a filter.

A user can provide the nonce by registering a filter.

function my_nonce_method(string|null $nonce): string|null
{
    return 'foo'; // Return the nonce value here.
}
add_filter('rollbar_js_nonce', my_nonce_method(...));

// Or in the traditional syntax...
add_filter('rollbar_js_nonce', 'my_nonce_method');

Unfortunately, because WordPress has no standard way to set a nonce attibute we can't provide a default value.

Type of change

• New feature (non-breaking change that adds functionality)

Related issues

• Fix Add nonce attribute to client side script #87

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer