build(netgo): make sure the project is always compiled with netgo build tag (#3428)

* build(netgo): make sure the project is always compiled with `netgo` build tag

* docs(netgo): better comments

conf/buildtags/buildtags.go

@@ -0,0 +1,4 @@
+package buildtags
+
+// This file is left intentionally empty. It is used to make sure the package is not empty, in the case all
+// required build tags are disabled.

conf/buildtags/netgo.go

@@ -0,0 +1,11 @@
+//go:build netgo
+
+package buildtags
+
+// NOTICE: This file was created to force the inclusion of the `netgo` tag when compiling the project.
+// If the tag is not included, the compilation will fail because this variable won't be defined, and the `main.go`
+// file requires it.
+
+// Why this tag is required? See https://github.com/navidrome/navidrome/issues/700
+
+var NETGO = true