Nudge users to enable incremental prebuilds when prebuilds duration is more than 10 minutes on average

Problem to solve

Currently, incremental prebuilds exist inside project settings as a toggle option users can enable for a project.

However, this feature is only referenced in one changelog entry[1] and slightly documented (see section in prebuilds docs).

See also relevant discussion (internal). Cc @atduarte @geropl @jankeromnes

Proposal

MVC Step 1

Similarly to https://github.com/gitpod-io/gitpod/issues/9232, we could detect when project prebuilds on average take longer than 10 minutes and nudge users to enable incremental prebuilds using an alert within the project prebuilds page.

We could use:

1. A help alert component if this contains simply a tip that does not take into account usage but promotes a new feature, etc.
2. An information alert component if this contains neutral information that could take into account product usage, etc.
3. A warning alert component to help a user avoid an issue, in case skipping this could lead to excessive charging, see relevant discussion (internal).

Help Alert	Information Alert	Warning Alert

MVC Step 2

Additionally, although prebuilds eventually will be available to enable only via Projects, we could surface a similar alert on the workspace start page for repositories that have not been added as projects yet, nudging users to create a project and enable incremental prebuilds.

TBD (To be discussed)

Start with the project prebuilds page and inspect how existing help, information, or warning alerts are implemented. Trace how average prebuild duration and incremental-prebuild settings are exposed, then determine the workspace start page path for repositories that are not projects. Done means the agreed alert appears for qualifying projects, with the second step resolved or explicitly scoped.