DRILL-7343: Add User-Agent UDFs to Drill

[cgivre]

These UDFs add the ability to parse user agent strings, which is useful for security data analysis.

[cgivre]

@KazydubB
What happens in the parse_query function is that there is a duplicate function of the same name which allows null input which returns an empty list. I had tried this before, but apparently didn't use the correct parameters so it didn't work for me, BUT, now it does so yay!

In any event, this seems like horrible design. I'm going to open a JIRA to create a new function handler which returns an empty list on null. That seems like a better approach than having to write 2 UDFS for every UDF with a complex writer output.

I also added a series of unit tests to test this functionality.

[KazydubB]

@cgivre I agree that having two functions for OPTIONAL and REQUIRED cases is not the best experience, but returning an empty list on NULL is not enough, because there may be functions that will need to return a MAP for example. So, there's a need to provide NullHandling for NULL input for other cases too (EMPTY_LIST_IF_NULL, EMPTY_MAP_IF_NULL etc.).

[cgivre]

@KazydubB I opened a JIRA for the null issues, but this PR should be ready to go.

[arina-ielchiieva]

@cgivre overall looks good, please fix minor remaining issues (including extra or missing spaces) and PR will be ready to go.

[arina-ielchiieva]

Looks good, +1