Provide informative error when pipelines build is hung caused by variable length

Issue Summary

Currently, when a build has multiple variables configured (including Repository Variables, Account Variables, Deployment Variables) and has a total of 120K characters combined, it could cause the pipelines build to be in a hung state.

This could be misleading as the actual error message isn't displayed nor informative.

A suggestion is to :

1. Include an informative message indicating that pipelines build failed for the reason.
2. Instead of allowing the build to be hung indefinitely until timeout, it's better if builds could be stopped / marked as failed.
3. Allow increase of variable length limit above 120k.