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>

api/publish.go

@@ -96,6 +96,7 @@ func apiPublishRepoOrSnapshot(c *gin.Context) {
 		ButAutomaticUpgrades string
 		ForceOverwrite       bool
 		SkipContents         *bool
+		SkipBz2              *bool
 		Architectures        []string
 		Signing              SigningOptions
 		AcquireByHash        *bool
@@ -209,6 +210,11 @@ func apiPublishRepoOrSnapshot(c *gin.Context) {
 			published.SkipContents = *b.SkipContents
 		}
 
+		published.SkipBz2 = context.Config().SkipBz2Publishing
+		if b.SkipContents != nil {
+			published.SkipBz2 = *b.SkipBz2
+		}
+
 		if b.AcquireByHash != nil {
 			published.AcquireByHash = *b.AcquireByHash
 		}
@@ -243,6 +249,7 @@ func apiPublishUpdateSwitch(c *gin.Context) {
 		ForceOverwrite bool
 		Signing        SigningOptions
 		SkipContents   *bool
+		SkipBz2        *bool
 		SkipCleanup    *bool
 		Snapshots      []struct {
 			Component string `binding:"required"`
@@ -322,6 +329,10 @@ func apiPublishUpdateSwitch(c *gin.Context) {
 		published.SkipContents = *b.SkipContents
 	}
 
+	if b.SkipBz2 != nil {
+		published.SkipBz2 = *b.SkipBz2
+	}
+
 	if b.AcquireByHash != nil {
 		published.AcquireByHash = *b.AcquireByHash
 	}