What was changed

This adds a default version, which will be used if someone builds tcld off of the main branch. We will still send the commit version, for logging purposes.

Why?

Ensure tcld can work with our API versioning in all cases.

Checklist

• Tested with go build ./cmd/tcld:

❯ ./tcld version
{
    "Date": "2023-09-06T18:33:22Z",
    "Commit": "dd1e2e99e590193980200ee6e7f4c7ea80d240be-modified",
    "Version": "v0.1.3-no-version-available"
}

• Tested with make (it picks up a pre-release version tag I used in GitHub for testing, since this branch is not a release):

❯ ./tcld version
{
    "Date": "2023-09-06T11:54:16-07:00",
    "Commit": "495416177a6d",
    "Version": "v0.13.1-embed-version-test"
}