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/golang/gddo/httputil/respbuf.go

@@ -0,0 +1,58 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd.
+
+package httputil
+
+import (
+	"bytes"
+	"net/http"
+	"strconv"
+)
+
+// ResponseBuffer is the current response being composed by its owner.
+// It implements http.ResponseWriter and io.WriterTo.
+type ResponseBuffer struct {
+	buf    bytes.Buffer
+	status int
+	header http.Header
+}
+
+// Write implements the http.ResponseWriter interface.
+func (rb *ResponseBuffer) Write(p []byte) (int, error) {
+	return rb.buf.Write(p)
+}
+
+// WriteHeader implements the http.ResponseWriter interface.
+func (rb *ResponseBuffer) WriteHeader(status int) {
+	rb.status = status
+}
+
+// Header implements the http.ResponseWriter interface.
+func (rb *ResponseBuffer) Header() http.Header {
+	if rb.header == nil {
+		rb.header = make(http.Header)
+	}
+	return rb.header
+}
+
+// WriteTo implements the io.WriterTo interface.
+func (rb *ResponseBuffer) WriteTo(w http.ResponseWriter) error {
+	for k, v := range rb.header {
+		w.Header()[k] = v
+	}
+	if rb.buf.Len() > 0 {
+		w.Header().Set("Content-Length", strconv.Itoa(rb.buf.Len()))
+	}
+	if rb.status != 0 {
+		w.WriteHeader(rb.status)
+	}
+	if rb.buf.Len() > 0 {
+		if _, err := w.Write(rb.buf.Bytes()); err != nil {
+			return err
+		}
+	}
+	return nil
+}