Allow nginx to cache logos

> curl -I https://membership.eclipse.org/organization/images/656-web.gif
> 
> HTTP/2 200
> server: nginx
> date: Thu, 11 Jul 2024 14:07:58 GMT
> content-type: image/gif
> content-length: 867
> last-modified: Thursday, 11-Jul-2024 14:09:17 UTC
> accept-ranges: bytes
> content-security-policy: frame-ancestors 'self'
> x-frame-options: SAMEORIGIN
> x-content-type-options: nosniff
> strict-transport-security: max-age=63072000; includeSubDomains; preload
> cache-control: no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0
> x-content-type-options: nosniff
> x-xss-protection: 1; mode=block
> x-proxy-cache: MISS

cache-control: no-store, no-cache, must-revalidate, proxy-revalidate, max-age=0

^ This is stopping nginx from caching the request. Improving this could reduce the load on NFS and make the membership site more stable.

To consider: Since our logo URLs remain unchanged with each update or upload, we will need to update our portal UI to append a random query string to these logos. This ensures that when a new logo is uploaded, the client sees the updated version instead of the cached one. For example: https://membership.eclipse.org/organization/images/656-web.gif?random_string.

Nginx will treat this as a different request and will fetch the latest version. The objective is not so much to cache the logo when users visit the portal (low traffic compared to our other sites), it's to ensure that it's cached when used across all our web properties such as eclipse.org, the working group website, and PMI.

/cc @droy