add giscus.app to CSP via .htaccess file

[kevinjqliu]

Relates to #80

Requires #106 to comply with ASF Content Security Policy

We still need to get blessing from privacy@apache.org before merging this PR

More info on Apache and CSP:

• https://infra.apache.org/tools/csp.html
• https://infra.apache.org/csp.html
• https://httpd.apache.org/docs/current/howto/htaccess.html
• https://github.com/giscus/giscus/blob/main/PRIVACY-POLICY.md

Examples:

• https://privacy.apache.org/examples/youtube-html/with-youtube-api.html
• https://github.com/apache/fluss/blob/main/website/.htaccess

[kevinjqliu]

remote: Permission to apache/datafusion-site.git denied to github-actions[bot].
fatal: unable to access 'https://github.com/apache/datafusion-site/': The requested URL returned error: 403
Error: Process completed with exit code 128.

oh right, i dont have permission

[kevinjqliu]

looking like the CI logs, seems like only the blogs/ dir is updated for staging..

[kevinjqliu]

if we have to update .htaccess file, i think we need to explicitly update the asf-site branch and/or the asf-staging branch

There files matches the asf-staging branch

• https://datafusion.staged.apache.org/.gitignore
• https://datafusion.staged.apache.org/.asf.yaml
• https://datafusion.staged.apache.org/.git/