Support AGENT_TOOLSDIRECTORY as in setup-python action

[th-le]

Description:

We needs to run a custom workflow to populate tools cache data for self-hosted runners. However it could not override the default downloading location on setup-node action.

Setup-python already has support for this use case. We'd like to have the same logic applied on this action.

Related issue: https://github.com/actions/setup-node/issues/1039

Check list:

• [ ] Mark if documentation changes are required.
• [ ] Mark if tests were added or updated to cover the changes.

[snwbr]

it would be good to review this one as it's a small yet an important one