Prepare for v0.13.0

[ktock]

• Should be merged after:
  • Bump k8s.io from 0.25.3 to 0.25.4 #994
  • Bump github.com/ipfs/go-ipfs-files from 0.1.1 to 0.2.0 #990
  • Dockerfile: Bump up Podman(v4.3.0), conmon(v2.1.5) #987

This release enables to optionallly create smaller eStargz images using the following flags for `ctr-rmeote i convert` or `ctr-remote i optimize` (#956).

- `--estargz-external-toc`: Separates TOC JSON into another image (called "TOC image"). The result eStargz doesn't contain TOC so we can expect a smaller size than normal eStargz (refer to [`/docs/estargz.md`](https://github.com/containerd/stargz-snapshotter/blob/v0.13.0/docs/estargz.md#estargz-image-with-an-external-toc-optional) for the related eStargz spec).
- `--estargz-min-chunk-size`: Specifies the minimal number of bytes of data must be written in one gzip stream. If it's > 0, multiple files and chunks can be written into one gzip stream. Smaller number of gzip header and smaller size of the result blob can be expected (refer to [`/docs/estargz.md`](https://github.com/containerd/stargz-snapshotter/blob/v0.13.0/docs/estargz.md#details-about-inneroffset) for the related eStargz spec).

Please refer to [`/docs/smaller-estargz.md`](https://github.com/containerd/stargz-snapshotter/blob/v0.13.0/docs/smaller-estargz.md) for more details about the usage.

## Notable Changes

- eStargz
  -  Support creating smaller eStargz images (`--estargz-external-toc` and `--estargz-min-chunk-size`) (#956)
- stargz-snapshotter
  - fs: Try unmount without MNT_FORCE before force unmount (#978)
  - remote: Support per-registry request headers (#983)
  - Allow using fusermount3 (#970)
- converter
  - zstdchunked: allows specifying compression level (#984)
- Kind image ([`ghcr.io/containerd/stargz-snapshotter:${VERSION}-kind`](https://github.com/containerd/stargz-snapshotter/pkgs/container/stargz-snapshotter))
  - Revert clone3-workaround (#967)
- CI
  - Bump nerdctl to 1.0.0 (#969), thanks to @jenting
- Documents
  -  Add document about integrations of eStargz with other tools ([`/docs/integration.md`](https://github.com/containerd/stargz-snapshotter/blob/v0.13.0/docs/integration.md)) (#995, #997), thanks to @gaius-qi