Add method to ProcessArgumentBuilder class to insert argument at any location

### What You Are Seeing?

Can't insert argument to a location in between the first and the last in ProcessArgumentBuilder.

### What is Expected?

I should be able to insert an argument at any location, not just first and last.

### What version of Cake are you using?

Latest

### How Did You Get This To Happen? (Steps to Reproduce)

When unsupported SignTool arguments are required - they can't be last or first.

Start by locating the ProcessArgumentBuilder class and reviewing how it currently handles insertion at the first and last positions. Add support for inserting an argument between existing arguments, including the unsupported SignTool argument case described here, and verify the behavior with the relevant test coverage if present.

Written by the indexing model from the issue text.