Add a route which returns the API version

[RemiBardon]

Sometimes @Paloma-Sanchez seems to have issues where she runs a Docker image but Dokcer uses an outdated version and bugs aren't fixed as expected. To help detecting this, I suggest we add a route which returns informations about the api version.

We should return the tag, but also the date at which the image was built, which is far easier to reason with.

Also, since we won't have the opportunity to return the current tag for edge and local builds, returning the build date will make total sense.

On the version information route, we could return an object like this:

{
    "version": "v0.4.0 (2025-01-01)",
    "tag": "v0.4.0",
    "build_date": "2025-01-01",
    "build_timestamp": "2025-01-01T22:12:00Z",
    "commit_short": "e3e6bbb",
    "commit_long": "e3e6bbba82fa0d1934990f878c1db376fc35f7d8"
}

This way, we'd support adding more keys in the future if needed.

For local builds, it could look like:

{
    "version": "local (2025-01-04)",
    "tag": "local",
    "build_date": "2025-01-04",
    "build_timestamp": "2025-01-04T11:09:00Z",
    "commit_short": null,
    "commit_long": null
}

(We might want to add commit information if there are no unstaged changes.)

Finally, for edge builds it'd look like this:

{
    "version": "edge (2025-01-01)",
    "tag": "edge",
    "build_date": "2025-01-01",
    "build_timestamp": "2025-01-01T22:15:00Z",
    "commit_short": "e3e6bbb",
    "commit_long": "e3e6bbba82fa0d1934990f878c1db376fc35f7d8"
}

---

Edit (2025-01-15):

We would like to access Prosody version information too, so to simplify parsing I suggest we switch to this more extensible structure:

{
    "self": {
        "version": "v0.4.0 (2025-01-01)",
        "tag": "v0.4.0",
        "build_date": "2025-01-01",
        "build_timestamp": "2025-01-01T22:12:00Z",
        "commit_short": "e3e6bbb",
        "commit_long": "e3e6bbba82fa0d1934990f878c1db376fc35f7d8"
    },
    "prosody": {
        "version": "...",
        "tag": "...",
        "build_date": "...",
        "build_timestamp": "...",
        "commit_short": "...",
        "commit_long": "..."
    }
}

I haven't thought about it that much but I suppose it will be a bit hard to get some of the information for Prosody. We might have more information about prose-pod-server (~prosody), but it will be complicated because it's not bundled with the API. The API could have this data passed staticly at build time but the version of Prosody running is dynamic.