Print plugin versions

[mavam]

📔 Description

The version command now prints the plugin version as follows:

{
  "VAST": "2020.12.16-97-gced115d91-dirty",
  "CAF": "0.17.6",
  "Apache Arrow": "2.0.0",
  "PCAP": "libpcap version 1.9.1",
  "jemalloc": null,
  "plugins": {
    "example": "0.0.0-0"
  }
}

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

In one shot.

[lava]

I fear this might be a bit premature, we probably need to work on the version concept a bit more before presenting it so prominently to users.

In particular, there are several relevant versions: The ABI version, relevant when loading the plugin (changes all the time), the API version of the VAST plugin API that the plugin was written against, relevant when compiling the plugin (expected to change frequently while the feature is experimental, relatively stable afterwards) and the finally the package version of the plugin itself, irrelevant to vast but relevant to any downstream users of the plugin.

The current version is laid out like the last one, with patch and tweak versions, but internally it's more used like the first two. We should probably think about which of these we want to collect and display, and how.

Edit: If the version is intended to be one the first two, we should also specify the semantics of the individual fields. (ie. what does a "patch" version number mean for an ABI version?)

[dominiklohmann]

Let's move forward with this as is. We decided to do versioning checks for libvast API and ABI separately. This version number is only user-facing.