Support for pages authentication switches

What does this MR do?

This merge request adds support for GitLab pages authentication switches implemented by @tuomoa in gitlab-pages!94 (merged).

Checklist

See Definition of done.

• Change added to CHANGELOG.md. Not applicable for Documentation changes and minor changes.
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA, if applicable
• MR targeting master branch
• MR has a green pipeline on GitLab.com

Reviewer Checklist

In addition to above, reviewer must:

• Pipeline is green on dev.gitlab.org if the change is not touching documentation or internal cookbooks

References

https://gitlab.com/gitlab-org/gitlab-ce/issues/33422

gitlab-pages!94 (merged)

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18589

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/33422

config/patches/libiconv/libiconv-1.14_srclib_stdio.in.h-remove-gets-declarations.patch

---- libiconv-1.14/srclib/stdio.in.h.orig  2014-07-02 01:49:41.484192961 +0000
-+++ libiconv-1.14/srclib/stdio.in.h 2014-07-02 01:51:10.433127793 +0000
-@@ -679,26 +679,6 @@
- # endif
- #endif
-
--#if @GNULIB_GETS@
--# if @REPLACE_STDIO_READ_FUNCS@ && @GNULIB_STDIO_H_NONBLOCKING@
--#  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
--#   undef gets
--#   define gets rpl_gets
--#  endif
--_GL_FUNCDECL_RPL (gets, char *, (char *s) _GL_ARG_NONNULL ((1)));
--_GL_CXXALIAS_RPL (gets, char *, (char *s));
--# else
--_GL_CXXALIAS_SYS (gets, char *, (char *s));
--#  undef gets
--# endif
--_GL_CXXALIASWARN (gets);
--/* It is very rare that the developer ever has full control of stdin,
--   so any use of gets warrants an unconditional warning.  Assume it is
--   always declared, since it is required by C89.  */
--_GL_WARN_ON_USE (gets, "gets is a security hole - use fgets instead");
--#endif
--
--
- #if @GNULIB_OBSTACK_PRINTF@ || @GNULIB_OBSTACK_PRINTF_POSIX@
- struct obstack;
- /* Grow an obstack with formatted output.  Return the number of