Automagically determine `install-tool` for `postUpgradeTasks` (based on repo)

[jamietanna]

Related: #8111

With existing updates we will detect the ToolConstraints needed to execute i.e. php, or composer.

We should provide (an opt-in?) means to install-tool based on this.

This will be after the implementation of ??

This could be via:

{
  "installTools": {
    "auto": {}
  }
}