Do mongo handshake and store ServerDescription on connection

[WebFreak001]

It seems not all types in the struct are used but this is required for future changes like server selection or changed APIs (see #2200)

Also makes the vibe app more distinguishable in the mongodb admin log because you know which application was doing stuff then.

[wilzbach]

Added a few initial comments.
Would be amazing to have a test for this.

[WebFreak001]

it would be amazing to have mongodb tests in general... we only have void test() in mongo unittest which is pretty useless for auto testing

[WebFreak001]

@wilzbach I have added a mongodb test runner now which contains the old mongodb unittest and now also a unittest testing several connection/auth methods. I couldn't get username/password auth to behave properly with vibe.d, it doesn't throw errors on login failure and it receives unknown data when trying to iterate over data. (both logged in and anonymous)

[WebFreak001]

bump @wilzbach @s-ludwig can I get a review on this, the better automated mongo tests and version information is pretty much a base for all other mongo features I had planned to add

[s-ludwig]

Once the tests pass, this can be merged from my side.

[WebFreak001]

are we sure the current mongodb login connection even works as expected? I modelled the exceptions that are supposed to be thrown after the mongo console behaviour and because there isn't thrown anything on failure it makes me think that maybe the insertion/removal code is missing checks for successful completion.

[WebFreak001]

@wilzbach

[wilzbach]

Could you rebase?

[WebFreak001]

bump, #2327 depends on this now

[wilzbach]

Thanks a lot for this essential work @WebFreak001, but as it touches a bit of the test system too, I prefer like to wait until @s-ludwig has had a chance to look over it too.

[WebFreak001]

bump, I think the current indexes code broke with MongoDB 4.2 now because #2327 is probably needed and this PR is needed to add the version-dependent code

[WebFreak001]

bump, tests passing now and all reviews handled in code now

[WebFreak001]

the changes aren't that much here, the tests and (de)serialization structs/enums which get handled automatically make up about 50%+20% of the PR.

Also there is added security and unittest on the sasl.d file which could really be moved into a separate PR but I don't think it hurts here. If that's the blocker, please tell me so I can move that to a separate PR.