gitlab: move docs and tools build across from Travis

While we are at it we might as well check the tag generation. For
bonus points we run GNU globals htags into the public pages directory
for publishing with the auto generated pages.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210114165730.31607-10-alex.bennee@linaro.org>