Add guidance on recommended architectures for smaller installations

Problem to solve

For customers who review our Scaling and High Availability page, it is not clear enough that they may not need scaling or HA if using GitLab with relatively few users compared to our existing Reference Architecture levels on that page (low end is 2,000 users). We should guide people to what's best for them, regardless of environment.

For example: Up to a limit of 100 or 1000 users, it can be sufficient to install Omnibus on a server and ensure you have backups.

Further details

Proposal

• Specify smaller-sized reference architectures, and how to choose whether you even need a scaled/HA architecture at all.
• Rework the page structure, intro and title to enable readers to start with a size and determine a solution. For example, perhaps the page itself should be named Reference Architectures or another more descriptive title that doesn't take use of Scaling and HA solutions for granted.
• Consider removing HA Architecture Examples and migrating the Scaling details into the reference architectures. Make clear that The core of a scaling vs. HA installation are the same. The only differences come from the backend services like Redis, DB, Consul, etc. If you don't need HA but need scaling, eliminate the HA in those backend pieces. Per #204997 (comment 286488596))

Who can address the issue

Other links/references

As originally raised in #204997 (closed)