Fix snake_case to camelCase in argline for csv and influxdb outputs

[mstoykov]

Throughout k6 we use camelCase for JSON options and CAPS_SNAKE_CASE for env variables. The few places where there are argline options such as k6 run -o csv=file_name=something.csv we sometimes use snake_case as in the CSV output and one option in the influxdb one, but sometimes we use camelCase as in the loki logs and the rest of the influxdb options :(.

Given that there really isn't a good case for one of the options to be camelCase and the other snake_case we should make them the same. For backwards compatible reasons we should still parse the snake_case variant and warn the user through a log message, at least for ... some versions.

So I propose that @codebien fixes the influxdb one in #2110 and there to be a separate PR for the CSV output.

[Sampriti-Mitra]

@mstoykov can I take this

[mstoykov]

Go for it @Sampriti-Mitra ! Just FYI if you want to do it as part of hacktoberfest, you might need to wait another 3 days or so, although maybe it's fine, I haven't really read the fine print 🤷‍♂️

[josephwoodward]

Hi @Sampriti-Mitra, are you working on this? If not I have a pull request here that I'd like to propose.

[Sampriti-Mitra]

@mstoykov sure, will be working on this!

[Sampriti-Mitra]

@josephwoodward think your PR looks good, @mstoykov can you assign this to @josephwoodward instead

[josephwoodward]

Hi, @mstoykov. I believe this issue can now be closed.

[na--]

The influxdb fixes are still pending in #2110, but there are other obstacles there, so there's no point in holding this up with them