contrib: add gorm.io/gorm

[AdallomRoy]

Fixes #684

[gbbr]

I recommend taking a look at other integrations to figure out what the style conventions and recommendations are for naming etc.

Once it's ready for review, just take it out of draft.

[AdallomRoy]

Thank you for your comments. I will first make sure all tests pass and then re-order everything to be according to your coding conventions

[AdallomRoy]

I'm pretty sure this is in accordance to your guidelines.
The tests that fail seem unrelated to my work, I'm not sure how stable the tests are normally, but please let me know if you think otherwise.

[gbbr]

Thanks for doing the work. You'll need to bear with us for a few more rounds of reviews but I think we're on the right path.

As for the CI test, no worries, we will look at that separately. It does seem unrelated to your PR. However, you will have to use gofmt on your code.

[gbbr]

CI is fixed. If you still plan on continuing the PR, once you rebase on v1 branch it should be fine (for the ci/circleci: test-contrib part)

[AdallomRoy]

Thanks!

[knusbaum]

Sorry, I've only now had a chance to take a look at this. Previously (in #714) I had looked into making a Plugin to add our tracing, as that looks like a simpler interface for the user. They would simply be able to write:

db.Use(gormtrace.Plugin())

@AdallomRoy What do you think about a Plugin? Do we lose anything by not using the Dialector interface?

[AdallomRoy]

Nice! I can check this out later this week and let you know