Add setProjectRootRegex method

[Cawllec]

Goal

Adds setProjectRootRegex to the Configuration class, allowing the projectRoot regex to be set directly.

Based on #501 by @jpcid, this adds additional tests and a dedicated method in the Client class to allow calling the added setProjectRootRegex method in the Configuration.

[kattrali]

Looks good aside from needing to handling strip path. It makes sense that the project root regex would be stripped from paths automatically, as that's how it works under the hood anyway for setProjectRoot().

[jpcid]

You guys are awesome! I was very busy last month and I did not have time to apply your feedback to the original PR

Thank you @kattrali and @Cawllec.