Backend: Allow Self Manage users to increase maximum number of includes

Problem

When building a CI/CD pipeline users often use the include keywords which reference external yaml configuration (file) in their CI/CD configuration. Users cannot have more than 150 includes per pipeline.

Proposal (for Self Manage users only)

Add an application limit setting for self-managed that allows them to have more than 150 includes.

Details:

Redefine the hardcoded limit with application limits application settings with 150 as the default recommended limit. With this thing in place, self-managed can set it to whatever works for their setup. For .com we should wait until the performance changes are implemented.

[2023-04-19] Proposal updated to use "application settings" (not limits) per #207270 (comment 1358530340).

Proposal for .com

A pre-requisite for .com is #382531 (closed) and #382751 (closed). Afterwards, we could increase the limit for .com.

Implementation

Description	MR
Allow max includes to be changed in application settings	!118392 (merged)

A new Maximum includes setting in Admin > Settings > CI/CD > Expand "Continuous Integration and Deployment" has been added to %16.0. You can also change ci_max_includes via the API.