Allow setting default parallel amount for each task

[koliveira15]

• I'd be willing to implement this feature (contributing guide)

Description

Add the ability to specify the number of default parallel projects per build task

Motivation

Some tasks require different default number of parallel executions. My test task might differ from my build task based on CI constraints.

Suggested Implementation

Leverage the new nx.json schema where each task has its own configuration. The default parallel property could be added here.

// nx.json
...
"targetDefaults": {
    "build": {
      "dependsOn": ["^build"],
      "inputs": ["production", "^production"],
      "cache": true,
      "parallel": 3
    },
    "test": {
      "inputs": ["default", "^production", "{workspaceRoot}/jest.preset.js"],
      "dependsOn": ["^test"],
      "cache": true,
      "parallel": 5
    }
  },
...

Alternate Implementations

[mattfysh]

To add another use case, I use the @wanews/nx-pulumi plugin in a number of projects and it requires stdin be inherited by the child process for interactive prompts. In CI environments it can run non-interactively, but when I'm developing I do want to interact with the task as it runs

This implementation would allow me to specify "parallel": 1 perhaps in nx.json, and ensure there is no stdin confusion

[FrozenPandaz]

Making this discussion to discuss more how people would like to configure this.