feat(Utils): Add validation to GetConfigurationValue

[Hipska]

Base information

Question	Answer
Related to a SourceForge thread / Another PR / Combodo ticket?	N/A
Type of change?	Enhancement

Objective

When retrieving settings, you sometimes need to additional type checking validation. The objective is to reduce this as much as possible.

Before:

$sStopOnError = Utils::GetConfigurationValue('stop_on_synchro_error', 'no');
if (($sStopOnError != 'yes') && ($sStopOnError != 'no')) {
	Utils::Log(LOG_WARNING, "Unexpected value '$sStopOnError' for the parameter 'stop_on_synchro_error'. Will NOT stop on error. The expected values for this parameter are 'yes' or 'no'.");
}
$bStopOnError = ($sStopOnError == 'yes');

After:

$bStopOnError = Utils::GetConfigurationValue('stop_on_synchro_error', 'no', FILTER_VALIDATE_BOOLEAN);

Proposed solution

Use php's integrated functionality to filter/validate variables by adding an optional filter flag to the GetConfigurationValue method. Current behaviour is not altered.

Checklist before requesting a review

• I have performed a self-review of my code, and that it's compliant with Combodo's guidelines
• I have tested all changes I made on an iTop instance
• I have added a unit test, otherwise I have explained why I couldn't
• I have made sure the PR is clear and detailled enough so anyone can understand the real purpose without digging in the code