Dump: add output format tar and output to stdout (#10376)

* Dump: Use mholt/archive/v3 to support tar including many compressions

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: Allow dump output to stdout

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: Fixed bug present since #6677 where SessionConfig.Provider is never "file"

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: never pack RepoRootPath, LFS.ContentPath and LogRootPath when they are below AppDataPath

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: also dump LFS (fixes #10058)

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Dump: never dump CustomPath if CustomPath is a subdir of or equal to AppDataPath (fixes #10365)

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* Use log.Info instead of fmt.Fprintf

Signed-off-by: Philipp Homann <homann.philipp@googlemail.com>

* import ordering

* make fmt

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Matti R <matti@mdranta.net>

vendor/github.com/mholt/archiver/v3/xz.go

@@ -0,0 +1,58 @@
+package archiver
+
+import (
+	"fmt"
+	"io"
+	"path/filepath"
+
+	"github.com/ulikunitz/xz"
+	fastxz "github.com/xi2/xz"
+)
+
+// Xz facilitates XZ compression.
+type Xz struct{}
+
+// Compress reads in, compresses it, and writes it to out.
+func (x *Xz) Compress(in io.Reader, out io.Writer) error {
+	w, err := xz.NewWriter(out)
+	if err != nil {
+		return err
+	}
+	defer w.Close()
+	_, err = io.Copy(w, in)
+	return err
+}
+
+// Decompress reads in, decompresses it, and writes it to out.
+func (x *Xz) Decompress(in io.Reader, out io.Writer) error {
+	r, err := fastxz.NewReader(in, 0)
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(out, r)
+	return err
+}
+
+// CheckExt ensures the file extension matches the format.
+func (x *Xz) CheckExt(filename string) error {
+	if filepath.Ext(filename) != ".xz" {
+		return fmt.Errorf("filename must have a .xz extension")
+	}
+	return nil
+}
+
+func (x *Xz) String() string { return "xz" }
+
+// NewXz returns a new, default instance ready to be customized and used.
+func NewXz() *Xz {
+	return new(Xz)
+}
+
+// Compile-time checks to ensure type implements desired interfaces.
+var (
+	_ = Compressor(new(Xz))
+	_ = Decompressor(new(Xz))
+)
+
+// DefaultXz is a default instance that is conveniently ready to use.
+var DefaultXz = NewXz()