Fix Catastophic Backtracking for Indirect Reference

[jpdakran]

Problem

• I've noticed that there is a hang when running detect-secrets.
• This is due to the regex that the Indirect-Reference filter utilizes.
• The problem here is catastrophic backtracking. This occurs when we are trying to match a line that is typically more than 25k characters against the regex.

Solution

• We have a few options here

1. Add conditions on when to run the regex for a line - 1k characters or less (or some agreed up length)
2. Update the regex

• I resorted to option 1. The intention of the heuristic should be for short and simple lines.

[domanchi]

@jpdakran : we should document design rationales in code to assist future developers in understanding the codebase.

[jpdakran]

Understood. Please see #516 for update.