timecraft: add get command

[achille-roussel]

This PR adds a new subcommand named timecraft get which displays the content of the time machine registry.

I implemented a tagging mechanism for objects stored in the registry, which should translate well to using resource tags of object storage on AWS/GCP.

Here are a few examples:

$ ./timecraft get mod
MODULE ID     MODULE NAME  SIZE
a11c1643e362  (none)       6.82 MiB

$ ./timecraft get mod -o json
{
  "mediaType": "application/vnd.timecraft.module.v1+wasm",
  "digest": "sha256:a11c1643e362e9fe0f0a40b45f0f2212e4a725ad8e969ce9fd7ff074cfe7e0d8",
  "size": 7150231,
  "annotations": {
    "timecraft.object.created-at": "2023-05-28T19:50:41Z",
    "timecraft.object.resource-type": "module"
  }
}

$ ./timecraft get mod -o yaml
mediaType: application/vnd.timecraft.module.v1+wasm
digest: sha256:a11c1643e362e9fe0f0a40b45f0f2212e4a725ad8e969ce9fd7ff074cfe7e0d8
size: 7150231
annotations:
  timecraft.object.created-at: "2023-05-28T19:50:41Z"
  timecraft.object.resource-type: module

I copied the human package from https://github.com/segmentio/cli into internal/print/human and made a few adjustments to improve the formatting of byte sizes and time/durations.

[achille-roussel]

I addressed all your feedback, thanks for the thorough review @chriso !