go/neo: Expand user prefix in TLS key/cert paths

This patch fixes a discrepancy between NEO/py and NEO/go: NEO/py expands
the '~' and the '~username' prefix in the file path of the TLS
certificate/key files [1]. This syntax is used in NEO/py SlapOS SR [2].
We need to fix this discrepancy in NEO/go in order to use TLS encryption
with NEO + WCFS.

[1] https://lab.nexedi.com/nexedi/neoppod/blob/7c539f0f/neo/lib/config.py#L149
and https://lab.nexedi.com/nexedi/neoppod/blob/fa63d856/neo/lib/app.py#L25-31

[2] https://lab.nexedi.com/nexedi/slapos/blob/397726e1/stack/erp5/instance-zodb-base.cfg.in#L18-20
and https://lab.nexedi.com/nexedi/slapos/blob/a8150a1a/software/neoppod/instance-neo-input-schema.json#L62

/reviewed-by @kirr
/reviewed-on !1

go/neo/neonet/net.go

-// Copyright (C) 2018-2020  Nexedi SA and Contributors.
+// Copyright (C) 2018-2023  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -30,6 +30,7 @@ import (
 	"lab.nexedi.com/kirr/go123/xnet/lonet"
 	"lab.nexedi.com/kirr/go123/xstrings"
 
+	"lab.nexedi.com/kirr/neo/go/neo/internal/xpath/xfilepath"
 	"lab.nexedi.com/kirr/neo/go/neo/internal/xtls"
 )
 
@@ -93,7 +94,10 @@ func Join(ctx context.Context, cfg Config) (net xnet.Networker, err error) {
 	}
 
 	if ssl {
-		tlsCfg, err := xtls.ConfigForP2P(cfg.CA, cfg.Cert, cfg.Key)
+		xu := xfilepath.ExpandUser // Expand user for compatibility with NEO/py:
+		//	https://lab.nexedi.com/nexedi/neoppod/blob/d5afef8e/neo/lib/config.py#L149
+		//	https://lab.nexedi.com/nexedi/neoppod/blob/d5afef8e/neo/lib/app.py#L25-31
+		tlsCfg, err := xtls.ConfigForP2P(xu(cfg.CA), xu(cfg.Cert), xu(cfg.Key))
 		if err != nil {
 			return nil, err
 		}