Add new command `nixos-rebuild list-generations`. It will show an output
like
```
$ nixos-rebuild list-generations
Generation Build-date NixOS version Kernel Configuration Revision Specialisations
52 (current) Fri 2023-08-18 08:17:27 23.11.20230817.0f46300 6.4.10 448160aeccf6a7184bd8a84290d527819f1c552c *
51 Mon 2023-08-07 17:56:41 23.11.20230807.31b1eed 6.4.8 99ef480007ca51e3d440aa4fa6558178d63f9c42 *
```
This also mentions the change in the upcoming release notes
cc625486c4