Don't 500 when pages tries to serve a chunked file

What does this MR do?

This MR adds proxy_http_version 1.1 to the nginx config for the Gitlab Pages reverse proxy. When Pages serves large files, it splits them up into chunked payloads, which nginx in HTTP 1.0 mode (the default) cannot deal with, causing a 502 Bad Gateway error.

Related issues

Closes gitlab#416803 (closed).

It may also close the following linked issues, but this has not been confirmed by those issues OPs (just by other users):

• gitlab#415934 (closed)
• gitlab#416258 (closed)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch. (At least, I think so.)
• Latest Merge Result pipeline is green.
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow.

For GitLab team members

If you don't have access to this, the reviewer should trigger these jobs for you during the review process.

• The manual Trigger:ee-package jobs have a green pipeline running against latest commit.
• If config/software or config/patches directories are changed, make sure the build-package-on-all-os job within the Trigger:ee-package downstream pipeline succeeded.
• If you are changing anything SSL related, then the Trigger:package:fips manual job within the Trigger:ee-package downstream pipeline must succeed.
• If CI configuration is changed, the branch must be pushed to dev.gitlab.org to confirm regular branch builds aren't broken.

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.

Seems my original ticket gitlab#416803 (closed) works as a test plan.

• Documentation created/updated.
• Tests added.
• Integration tests added to GitLab QA.

This bug appears to be covered by existing tests, since one of the related issues gitlab#415934 (closed) was reported by Gitlab QA staff.

• Equivalent MR/issue for the GitLab Chart opened.

I am unfamiliar with that codebase, and searching it for instances of proxy_pass did not yield anything that looks relevant. Perhaps someone who uses this distribution could contribute one; I'll happily edit this description to link.

• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.

User configuration unchanged.