Node20 build configuration

[merlynomsft]

Description: Add Node20 build configuration for a batch of tasks

Update buildconfiggen to only update new build configuration (for Node20) without bumping existing tasks

Note: the most robust way to view this pr is on github.dev: https://github.dev/microsoft/azure-pipelines-tasks/pull/19008

A few items 'to-do' will be addressed in future PRs:

1. Need to update check-downgrading.js to handle retaining 'base' task versioning, aligned with changes to buildconfiggen
2. Update dependent libraries to node 20; e.g. azure-pipelines-task-lib, azure-pipelines-tasks-securefiles-common, etc

Documentation changes required: (Y/N) N

Added unit tests: (Y/N) N

Attached related issue: (Y/N) N

Checklist:

• Task version was bumped - please check instruction how to do it
• Checked that applied changes work as expected

[merlynomsft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 4 pipeline(s).