ADD stale bot

[philschmid]

Adds a stale bot that runs every day and comments on issue which are stale (no communication for 30 days) and closes them then after 7 more days.

Excluded issues with the following tag:

LABELS_TO_EXEMPT = [
    "bug",
    "feature request",
    "new model",
    "wip",
]

[JingyaHuang]

LGTM, thanks for adding it!

[JingyaHuang]

Seems this one introduced a styling issue:

Run source venv/bin/activate
warning: `ruff <path>` is deprecated. Use `ruff check <path>` instead.
tools/stale.py:1[9](https://github.com/huggingface/optimum-neuron/actions/runs/8465382921/job/23191938905#step:7:10):1: I001 [*] Import block is un-sorted or un-formatted
tools/stale.py:41:20: C414 Unnecessary `list` call within `sorted()`
Found 2 errors.
[*] 1 fixable with the `--fix` option (1 hidden fix can be enabled with the `--unsafe-fixes` option).
Error: Process completed with exit code 1.

On my way to fix it, once we merge the caching PR.