chore(all): memory and thread safe storage

- settings: get filter choices from storage for settings validation
- updater: update servers to the storage
- storage: minimal deep copying and data duplication
- storage: add merged servers mutex for thread safety
- connection: filter servers in storage
- formatter: format servers to Markdown in storage
- PIA: get server by name from storage directly
- Updater: get servers count from storage directly
- Updater: equality check done in storage, fix #882

internal/provider/privateinternetaccess/connection.go

@@ -2,6 +2,7 @@ package privateinternetaccess
 
 import (
 	"github.com/qdm12/gluetun/internal/configuration/settings"
+	"github.com/qdm12/gluetun/internal/constants/providers"
 	"github.com/qdm12/gluetun/internal/models"
 	"github.com/qdm12/gluetun/internal/provider/privateinternetaccess/presets"
 	"github.com/qdm12/gluetun/internal/provider/utils"
@@ -20,5 +21,6 @@ func (p *Provider) GetConnection(selection settings.ServerSelection) (
 		defaults.OpenVPNUDPPort = 1197
 	}
 
-	return utils.GetConnection(p.servers, selection, defaults, p.randSource)
+	return utils.GetConnection(providers.PrivateInternetAccess,
+		p.storage, selection, defaults, p.randSource)
 }