Feature - Pagination for git tree API

[richmahn]

Issue #5837

This PR adds pagination to the repos/{owner}/{repo}/git/trees/{sha} API to not have the restriction Github has truncating to the first 1000 entries and not show any more (GitHub docs say to see all files of big repos you'll have to clone the repo, yet we are trying to avoid that in our mobile app).

Now if you add ?page=2 (page is 1 when not given) as a query parameter it will show the next page. If there are still more items after the specified page, truncated will remain as true, when it is the last page, truncated will be false.

Also adds per_page= where per_page is how many items to show per page. Default is 1000 and is settable in the app.ini file as DFAULT_GIT_TREES_PER_PAGE

This PR also adds to the API docs the recursive=1 and this page=# query parameters for this API call.

Testing:
Can be tested with a repo with lots of files, such as https://git.door43.org/unfoldingWord/en_ugl/ and then once ported into a repo fo the same name of your localhost root user, curl --request GET --url "http://localhost:3000/api/v1/repos/root/en_ugl/git/trees/master?recursive=1&page=2" for the 2nd page (curl --request GET --url "http://localhost:3000/api/v1/repos/root/en_ugl/git/trees/master?recursive=1&page=30" for the last page, and if you do page 31 you should get a tree that is null)

[techknowlogick]

Please run make fmt and commit changes.

[techknowlogick]

Please add per_page param as well, see #5831 for an example

[richmahn]

@techknowlogick Both your requests done. While I know Chinese, I didn't update the Chinese version of the cheat-sheet like the example you gave me. Hopefully picked an ok name for this additional paging num setting but made it different to not be confused with the one from your example.

[lunny]

@richmahn I think we should start page from 1 not 0 since every other place did that.

[lunny]

And the CI failed.

[lafriks]

To fix CI run:

make generate-swagger

[richmahn]

@lunny ok, fixed and fixed.

[codecov-io]

Codecov Report

Merging #5838 into master will increase coverage by 0.08%.
The diff coverage is 45.83%.

@@            Coverage Diff             @@
##           master    #5838      +/-   ##
==========================================
+ Coverage   38.71%   38.79%   +0.08%     
==========================================
  Files         330      330              
  Lines       48697    48729      +32     
==========================================
+ Hits        18853    18906      +53     
+ Misses      27115    27083      -32     
- Partials     2729     2740      +11

Impacted Files	Coverage Δ
modules/setting/setting.go	51.77% <ø> (ø)	⬆️
routers/api/v1/repo/tree.go	41.12% <45.83%> (+41.12%)	⬆️
models/unit.go	14.28% <0%> (+14.28%)	⬆️

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[techknowlogick]

@richmahn to update vendor Gopkg.toml (and related files) the command to run is dep ensure -update code.gitea.io/sdk

[lafriks]

@zeripath need your review