Replace MustCompile with Compile for non-hardcoded regexes

[thepetk]

What does this PR do?

There are two cases that we are compiling a regex with regexp.MustCompile and a dynamic string:

One, for express js port detection

func getPortGroup(content string, matchIndexes []int, portPlaceholder string) string {
	contentBeforeMatch := content[0:matchIndexes[0]]
	re := regexp.MustCompile(`(let|const|var)\s+` + portPlaceholder + `\s*=\s*([^;]*)`)
	return utils.FindPotentialPortGroup(re, contentBeforeMatch, 2)
}

Second, for nodejs_detector.getPortFromScript() func:

for _, regex := range regexes {
	re := regexp.MustCompile(regex)
	port := utils.FindPortSubmatch(re, getScript(packageJson), 1)
	if port != -1 {
		return port
	}
}

As MustCompile action for error is panic this PR replaces those two functions with Compile and handles any error case accordingly.

A test resource is added along with the TestComponentDetectionOnExpress test, ensuring that a failure with regexp.Compile will be handled and the code will not panic.

Which issue(s) does this PR fix

fixes #220

PR acceptance criteria

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Unit/Functional tests

• Documentation

How to test changes / Special notes to the reviewer

The repo that this issue was first seen was the one mentioned inside the issue: https://github.com/backstage/backstage.