Add initial support of device posture checks (#1540)

This PR implements the following posture checks:

* Agent minimum version allowed
* OS minimum version allowed
* Geo-location based on connection IP

For the geo-based location, we rely on GeoLite2 databases which are free IP geolocation databases. MaxMind was tested and we provide a script that easily allows to download of all necessary files, see infrastructure_files/download-geolite2.sh.

The OpenAPI spec should extensively cover the life cycle of current version posture checks.

client/system/info.go

@@ -23,7 +23,6 @@ const OsNameCtxKey = "OsName"
 type Info struct {
 	GoOS               string
 	Kernel             string
-	Core               string
 	Platform           string
 	OS                 string
 	OSVersion          string
@@ -31,6 +30,7 @@ type Info struct {
 	CPUs               int
 	WiretrusteeVersion string
 	UIVersion          string
+	KernelVersion      string
 }
 
 // extractUserAgent extracts Netbird's agent (client) name and version from the outgoing context