Remove the use of the future module (backport #1366)

[mergify]

This module is buggy with Python 3.11 and 3.12, and is being actively removed from distributions (like Debian and Ubuntu). The absolute_import things are remaining of the past, in the Python 2.7 age. Let's get rid of them and remove future from setup.cfg.

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This is an automatic backport of pull request #1366 done by Mergify.

[mergify]

Cherry-pick of fa7d13d has failed:

On branch mergify/bp/stable/4.6/pr-1366
Your branch is up to date with 'origin/stable/4.6'.

You are currently cherry-picking commit fa7d13d4.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   gnocchi/common/redis.py
	modified:   gnocchi/indexer/sqlalchemy.py
	modified:   gnocchi/indexer/sqlalchemy_base.py
	modified:   gnocchi/indexer/sqlalchemy_extension.py
	modified:   gnocchi/indexer/sqlalchemy_types.py
	modified:   gnocchi/tests/functional/fixtures.py
	modified:   setup.cfg

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   gnocchi/gendoc.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[tobias-urdin]

@Mergifyio rebase

[mergify]

rebase

✅ Branch has been successfully rebased