Fine grain concurrency control

[unional]

Different tasks have different concurrency characteristics.
Some are light weight that many tasks can be run at the same time,
while some are heavy and should be limited.

Currently, we can only turn on or off concurrency that the task level.

It would be great that if we can control the concurrency limit for each task.

For example, while setting the overall concurrency to 4, limit test to 2.

This mean there can be 4 tasks running at the same time, only 2 of them can be the test task.

Also, rather than setting the concurrency to a specific value, it would be great if it can support percentage such as 80% or 25%, representing a percentage of the total core/thread available. This is the same support in turborepo

[milesj]

These are good ideas, I'll look into.