[rest] Fix content-security-policy violation on RestCatalog API yaml

[liyubin117]

Purpose

Apache webserver specifies a CSP in the HTTP header, making the CSP defined in the <meta> tag invalid. Therefore, we should not access rest-catalog-open-api.yaml via an external link.

Tests

API and Format

Documentation

[liyubin117]

@JingsongLi I have used csp in my local environment to test the feature and work fine, PTAL, thanks!

 <meta
          http-equiv="Content-Security-Policy"
          content="default-src 'self' data: blob: 'unsafe-inline' https://www.apachecon.com/ https://www.communityovercode.org/ https://analytics.apache.org/; script-src 'self' 'unsafe-inline' 'unsafe-eval' https://www.apachecon.com/ https://*.apache.org/ https://apache.org/; style-src 'self' 'unsafe-inline' data: https://*.apache.org/ https://apache.org/; frame-ancestors 'self'; frame-src 'self' data: blob:; img-src 'self' data: https://*.apache.org/ https://apache.org/ https://www.apachecon.com/; worker-src 'self' data: blob:;">

[JingsongLi]

Looks good to me!