Add validation of custom grok patterns file

Context

The support of custom grok patterns was added in #15

Just add the directory with name Patterns and a file (the file name doesn’t matter) with your own patterns.

Like Patterns\grok-custom-patterns:

ZIPCODE [1-9]{1}[0-9]{2}\s{0,1}[0-9]{3}

and use:

Grok grok = new Grok("%{ZIPCODE:zipcode}:%{EMAILADDRESS:email}");
var grokResult = grok.Parse($"122001:[e-mail]");

IndexOutOfRangeException

There is an issue when that custom file has the wrong content.

How to reproduce

Add to the Patterns\grok-custom-patterns the following data:

pattern

How to fix

Add some validation on load of custom grok file content. It should be pattern name, space, then the regexp for that pattern

[ManasviGoyal]

Hi @ManasviGoyal, are you still working on that?

I am busy with some work this month. You can can assign it someone else. No issue with me.

[Marusyk]

Hi @MazixM and @GioMaz, Thanks for your interest. You need to create a Pull Request with changes. Then we can choose the best one