Feature/load overlays

[SebastianSchildt]

Add support to overlay several VSS models. New parameter --overlays expecting a directory. All *.json files will be applied in alphanumeric order.

The effect is the same, as authenticated and adding the files via updateVSSTree, but it happens automatically at server start (terminating in case of any problems), so it is possible to refrain from doing this potentially dangerous and complex operations during runtime.

This will close #177

Also this changed the log level for applying a default from INFO to VERBOSE

[wenwenchenbosch]

why sort?

[SebastianSchildt]

Because the resulting VSS tree depends on the order the VSS files are merged. So the documentation (--help) states will be merged in "alphanumeric order". This sorts the detected filenames (it is not defined in what order we get them, when just iterating directory entries)

[wenwenchenbosch]

tested and it works. only a doubts: Is it meaningful to consider all *.json file of the given folder?

For testing, I have a json file created in the given folder:

> cat test.json 
{
    "bla": "blu"
}

Then

Test Client> getMetaData bla
{
    "action": "getMetaData", 
    "metadata": {
        "bla": "blu"
    }, 
    "requestId": "6f19c09f-dafe-4f36-a4a8-29cf5ac5caca", 
    "ts": "2021-09-24T12:24:11.1632482651Z"
}

it is also perfectly merged. but it may be somehow unexpected.

Maybe better to support list of file with wildcard support like --overlay myfolder/vss_*.json