Purge modified files from CDN Cache

[laukstein]

do-spaces-action successfully uploads files but doesn't purge it from DigitalOcean CDN Cache.

Can do it like

curl -X DELETE -H "Content-Type: application/json" \
    -H "Authorization: Bearer $DIGITALOCEAN_TOKEN" \
    -d '{"files": ["assets/img/hero.png","assets/css/*"]}}' \
    "https://api.digitalocean.com/v2/cdn/endpoints/<CDN_ENDPOINT_ID>/cache" 

API doc in https://docs.digitalocean.com/reference/api/api-reference/#operation/purge_cdn_cache
Example https://www.digitalocean.com/community/questions/api-to-purge-file-cache-from-spaces-cdn-after-file-update?comment=153381

[BetaHuhn]

Good point, we should definitely add this.

Feel free to create a PR for this (maybe use node-fetch instead of calling curl) and I will review and merge it.