More support for keyset pagination

[ericfrederich]

Description of the problem, including code/CLI snippet

Initial keyset pagination support was added in commit 0b71ba4, however it is still not:

• supported from CLI
• able to be set globally in configuration.

gitlab -o json project list --all --pagination keyset --order-by id

Expected Behavior

Pagination should be able to be set in the following places in order of precedence:

• cli argument
• via config file under a particular gitlab id
• via config under global section

Actual Behavior

Pagination can only be set in config file under a particular gitlab id.

Specifications

• python-gitlab version: master branch
• API version you are using (v3/v4): v4
• Gitlab server version (or gitlab.com): 13.2.3

[max-wittig]

As mentioned before:

• We cannot set it globally, as some people still rely on X-Total (bad!)
• We would keep a list of supported keyset endpoint (effort wise not that bad)

Keeping it open for now and let's see what GitLab does. I don't think we should do anything right now or break peoples workflow ☹️

[mitar]

So x-total header is not returned on gitlab.com when results have more than 10k results: https://docs.gitlab.com/ee/user/gitlab_com/index.html#pagination-response-headers

This makes things break in strange ways for code which works for some time, but then results grow to more than 10k and it stops working. I think this library should simply not encourage use of x-total pagination at all, or at least make it so that you have to opt-in if you really know what you are doing.

@ericfrederich See also #961.