fix: [torrust#581] update Index config files

New changes have been made to the Torrust Index config file. Some API endpoints exposing the configuration have also changed.
This commits only cahnges the config files. Later commits will udpate
other parts.

```toml
[logging]
log_level = "info"

[tracker]
mode = "public"
```

```toml
version = "2"

[logging]
threshold = "info"

[tracker]
private = false
listed = false
```

share/default/config/index.private.e2e.container.sqlite3.toml

@@ -1,6 +1,8 @@
+version = "2"
+
 [tracker]
 api_url = "http://tracker:1212"
-mode = "private"
+private = true
 url = "http://tracker:7070"
 
 [database]

share/default/config/index.public.e2e.container.sqlite3.toml

@@ -1,5 +1,8 @@
+version = "2"
+
 [tracker]
 api_url = "http://tracker:1212"
+private = false
 url = "udp://tracker:6969"
 
 [database]