[sshshim] persist debug file output with size limit (#549)

## Summary

This PR employs the `lumberjack` library to do log file rotation and
size limiting.

Previously, the log file would get truncated on each `sshshim` command
execution.

Now, it acts like a sane log file: 
1. logs get added to it across multiple command executions
2. when it hits the 2MB size limit, it gets rotated: 
   - rotation copies to a backup file and the log file is truncated.

This will help us in debugging issues with premature mutagen session
termination. We can inspect the logs to understand why sshshim thought
that it should terminate the connections for the VM.

## How was it tested?

1. created a 2MB fake log file: `yes "this is test file" | head -c
2000000 > test.file` and copied it to
`~/.config/devbox/ssh/shims/logs.txt`
2. triggered an ssh shim command (`devbox cloud shell`) a few times.
3. observed the file get rotated:
```
❯ ls -al ~/.config/devbox/ssh/shims/
total 24
drwxr--r--  6 savil  staff   192 Jan 27 14:48 .
drwx------  8 savil  staff   256 Jan 27 14:48 ..
-rw-r--r--  1 savil  staff  4901 Jan 27 14:48 logs-2023-01-27T22-48-47.703.txt.gz
-rw-r--r--  1 savil  staff  1085 Jan 27 14:48 logs.txt
lrwxr-xr-x  1 savil  staff    30 Jan 27 14:48 scp -> /Users/savil/golang/bin/devbox
lrwxr-xr-x  1 savil  staff    30 Jan 27 14:48 ssh -> /Users/savil/golang/bin/devbox
```

Author: savil

go.mod

@@ -31,6 +31,7 @@ require (
 	github.com/stretchr/testify v1.8.0
 	golang.org/x/exp v0.0.0-20221109205753-fc8884afc316
 	golang.org/x/mod v0.7.0
+	gopkg.in/natefinch/lumberjack.v2 v2.0.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 

go.sum

@@ -2,6 +2,7 @@ cuelang.org/go v0.4.3 h1:W3oBBjDTm7+IZfCKZAmC8uDG0eYfJL4Pp/xbbCMKaVo=
 cuelang.org/go v0.4.3/go.mod h1:7805vR9H+VoBNdWFdI7jyDR3QLUPp4+naHfbcgp55HI=
 github.com/AlecAivazis/survey/v2 v2.3.6 h1:NvTuVHISgTHEHeBFqt6BHOe4Ny/NwGZr7w+F8S9ziyw=
 github.com/AlecAivazis/survey/v2 v2.3.6/go.mod h1:4AuI9b7RjAR+G7v9+C4YSlX/YL3K3cWNXgWXOhllqvI=
+github.com/BurntSushi/toml v1.2.0 h1:Rt8g24XnyGTyglgET/PRUNlrUeu9F5L+7FilkXfZgs0=
 github.com/MakeNowJust/heredoc/v2 v2.0.1 h1:rlCHh70XXXv7toz95ajQWOWQnN4WNLt0TdpZYIR/J6A=
 github.com/MakeNowJust/heredoc/v2 v2.0.1/go.mod h1:6/2Abh5s+hc3g9nbWLe9ObDIOhaRrqsyY9MWy+4JdRM=
 github.com/Netflix/go-expect v0.0.0-20220104043353-73e0943537d2 h1:+vx7roKuyA63nhn5WAunQHLTznkw5W8b1Xc0dNjp83s=
@@ -152,6 +153,9 @@ golang.org/x/text v0.5.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20200227125254-8fa46927fb4f h1:BLraFXnmrev5lT+xlilqcH8XK9/i0At2xKjWk4p6zsU=
+gopkg.in/natefinch/lumberjack.v2 v2.0.0 h1:1Lc07Kr7qY4U2YPouBjpCLxpiyxIVoxqXgkXLknAOE8=
+gopkg.in/natefinch/lumberjack.v2 v2.0.0/go.mod h1:l0ndWWf7gzL7RNwBG7wST/UCcT4T24xpD6X8LsfU/+k=
+gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.0/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

internal/cloud/openssh/sshshim/logger.go

@@ -12,14 +12,15 @@ import (
 	"github.com/pkg/errors"
 	"go.jetpack.io/devbox/internal/cloud/mutagenbox"
 	"go.jetpack.io/devbox/internal/debug"
+	"gopkg.in/natefinch/lumberjack.v2"
 )
 
 const (
 	logFileName = "logs.txt"
 )
 
 func EnableDebug() {
-	if w, err := logFile(); err == nil {
+	if w, err := logFileWriter(); err == nil {
 		debug.SetOutput(w)
 	} else {
 		fmt.Fprintf(os.Stderr, "failed to init ssh log file: %s", err)
@@ -29,22 +30,17 @@ func EnableDebug() {
 }
 
 // logFile captures output for logging and when there is a failure
-// NOTE: Ideally, we should limit the size of this log file, but it is always truncated
-// because only the last ssh invocation (which may have failed) has its output saved.
-// So size should hopefully not be crazy big.
-func logFile() (io.Writer, error) {
+func logFileWriter() (io.Writer, error) {
 	dirPath, err := mutagenbox.ShimDir()
 	if err != nil {
 		return nil, errors.WithStack(err)
 	}
 
-	file, err := os.OpenFile(
-		filepath.Join(dirPath, logFileName),
-		os.O_RDWR|os.O_CREATE|os.O_TRUNC,
-		0700,
-	)
-	if err != nil {
-		return nil, errors.WithStack(err)
-	}
-	return file, nil
+	return &lumberjack.Logger{
+		Filename:   filepath.Join(dirPath, logFileName),
+		MaxSize:    2, // megabytes
+		MaxBackups: 2,
+		MaxAge:     28,   // days
+		Compress:   true, // disabled by default
+	}, nil
 }