Allow disabling bzip2 compression for index files

Using bzip2 generates smaller index files (roughly 20% smaller Packages
files) but it comes with a big performance penalty.  When publishing a
debian mirror snapshot (amd64, arm64, armhf, source) without contents
skipping bzip speeds things up around 1.8 times.

```
$ hyperfine -w 1 -L skip-bz2 true,false  -m 3 -p "aptly -config aptly.conf publish drop bullseye || true" "aptly -config aptly.conf  publish snapshot  --skip-bz2={skip-bz2} --skip-contents --skip-signing bullseye"
Benchmark 1: aptly -config aptly.conf  publish snapshot  --skip-bz2=true --skip-contents --skip-signing bullseye
  Time (mean ± σ):     35.567 s ±  0.307 s    [User: 39.366 s, System: 10.075 s]
  Range (min … max):   35.311 s … 35.907 s    3 runs

Benchmark 2: aptly -config aptly.conf  publish snapshot  --skip-bz2=false --skip-contents --skip-signing bullseye
  Time (mean ± σ):     64.740 s ±  0.135 s    [User: 68.565 s, System: 10.129 s]
  Range (min … max):   64.596 s … 64.862 s    3 runs

Summary
  'aptly -config aptly.conf  publish snapshot  --skip-bz2=true --skip-contents --skip-signing bullseye' ran
    1.82 ± 0.02 times faster than 'aptly -config aptly.conf  publish snapshot  --skip-bz2=false --skip-contents --skip-signing bullseye'
```

Allow skipping bz2 creation for setups where faster publishing is more
important then Package file size.

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>

deb/index_files.go

@@ -22,6 +22,7 @@ type indexFiles struct {
 	suffix           string
 	indexes          map[string]*indexFile
 	acquireByHash    bool
+	skipBz2          bool
 }
 
 type indexFile struct {
@@ -68,7 +69,7 @@ func (file *indexFile) Finalize(signer pgp.Signer) error {
 	}
 
 	if file.compressable {
-		err = utils.CompressFile(file.tempFile, file.onlyGzip)
+		err = utils.CompressFile(file.tempFile, file.onlyGzip || file.parent.skipBz2)
 		if err != nil {
 			file.tempFile.Close()
 			return fmt.Errorf("unable to compress index file: %s", err)
@@ -80,11 +81,15 @@ func (file *indexFile) Finalize(signer pgp.Signer) error {
 	exts := []string{""}
 	cksumExts := exts
 	if file.compressable {
-		exts = append(exts, ".gz", ".bz2")
-		cksumExts = exts
 		if file.onlyGzip {
 			exts = []string{".gz"}
 			cksumExts = []string{"", ".gz"}
+		} else {
+			exts = append(exts, ".gz")
+			if !file.parent.skipBz2 {
+				exts = append(exts, ".bz2")
+			}
+			cksumExts = exts
 		}
 	}
 
@@ -229,7 +234,7 @@ func packageIndexByHash(file *indexFile, ext string, hash string, sum string) er
 	return nil
 }
 
-func newIndexFiles(publishedStorage aptly.PublishedStorage, basePath, tempDir, suffix string, acquireByHash bool) *indexFiles {
+func newIndexFiles(publishedStorage aptly.PublishedStorage, basePath, tempDir, suffix string, acquireByHash bool, skipBz2 bool) *indexFiles {
 	return &indexFiles{
 		publishedStorage: publishedStorage,
 		basePath:         basePath,
@@ -239,6 +244,7 @@ func newIndexFiles(publishedStorage aptly.PublishedStorage, basePath, tempDir, s
 		suffix:           suffix,
 		indexes:          make(map[string]*indexFile),
 		acquireByHash:    acquireByHash,
+		skipBz2:          skipBz2,
 	}
 }
 

deb/publish.go

@@ -62,6 +62,9 @@ type PublishedRepo struct {
 	// Skip contents generation
 	SkipContents bool
 
+	// Skip bz2 compression for index files
+	SkipBz2 bool
+
 	// True if repo is being re-published
 	rePublishing bool
 
@@ -585,7 +588,7 @@ func (p *PublishedRepo) Publish(packagePool aptly.PackagePool, publishedStorageP
 	}
 	defer os.RemoveAll(tempDir)
 
-	indexes := newIndexFiles(publishedStorage, basePath, tempDir, suffix, p.AcquireByHash)
+	indexes := newIndexFiles(publishedStorage, basePath, tempDir, suffix, p.AcquireByHash, p.SkipBz2)
 
 	legacyContentIndexes := map[string]*ContentsIndex{}
 	var count int64