Enable "v4" API namespace

added 3 commits

67a917a6 - Add new v4 namespace support
44d71f1b - Pass current version as default for api helper method
3c097a53 - Ignore iid param for issues filter on v4

@smcgivern Still unfinished, but could you give a quick look?

Still couldn't figure out how we'll make the conditional "fall up" from v3 -> v4 with Grape, though with this approach we can work with v3 and v4 separately, and on demand.

cc: @razer6 @to1ne

This seems OK to me. Just to clarify, does only code that is different in v4 end up in lib/api/v4? Other than that, do we just have lib/api mean v4, and lib/api/v3 mean v3-specific stuff?

Falling up is a nice-to-have. If we have to literally copy the code and specs, I can deal with that, it's just more work.

@smcgivern @oswaldo Ideally this is what would be my ideal solution:

Copy the code & specs that will change in v4 to v3 subdirectory
Modify existing code & specs to work according v4
Avoid splitting up code (e.g. the IssuesHelpers) for temporary double use

I don't mind duplicating code (only for this purpose), because the code will be deleted at some point. I think it is more important to make it easy (and without risk) to delete v3 when we want, and to have a clean codebase afterward.

I've also made an attempt to implement the parallel v3 and v4 namespaces in tc-v4-api-namespace.

@smcgivern That's the idea. Clarifying:

V3 namespace: Only v3 specific
V4 namespace: Only v4 specific
Common namespace (e.g.: lib/api/issues.rb), used by both

But I'm also OK on duplicating that, as @to1ne said, it will be a smooth v3 removal after all.

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2f636978 - Ignore iid param for issues filter on v4

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47d63db7 - Ignore iid param for issues filter on v4

Compare with previous version

Changed following @to1ne idea. What we've got here so far:

"Fall up" from v3 to v4 when endpoint not found on v3
V4 namespace stays the same and we can work on breaking change there (always copying all v3 endpoints to the new namespace, keeping it unchanged)
All tests run's on v4 by default

One thing we could decide here is, or we literally also copy v3 tests to a new file, or we just separate the v3 old behavior on a new context/describe.

cc: @razer6 @smcgivern