Trim the amount of prebuilds surfacing the dashboard

[gtsiolis]

Problem

The upcoming Teams & Projects feature will surface prebuilds in the dashboard. However, this is still not optimized to fetch all prebuilds, see #5038

For example, see https://gitpod-staging.com/gitpod-io/gitpod/prebuilds (internal).

Proposal

Before improving the performance for fetching prebuilds or adding any kind of pagination, we could just trim the amount of prebuilds surfacing the dashboard to 10 or 20 items similar to the branches list.

[AlexTugarev]

this is quite bad and results in an empty rendering.