Add Cloud Elevator pitch on Cloud Service pages

The Cloud Elevator Pitch is final.

It can replace the former formulation:

• https://hifis.net/services/
• https://hifis.net/services/cloud/Helmholtz_cloud.html

assigned to @SpickerHZB

created merge request !321 (merged) to address this issue

mentioned in merge request !321 (merged)

closed with merge request !321 (merged)

mentioned in commit 903c74f2