fix: replace moby/moby namesgenerator with internal implementation (#21377)

Replace the external moby/moby/pkg/namesgenerator dependency with an
internal implementation using gofakeit/v7. The moby package has ~25k
unique name combinations, and with its retry parameter only adds a
random digit 0-9, giving ~250k possibilities. In parallel tests, this
has led to collisions (flakes).

The new internal API at coderd/util/namesgenerator eliminates the
external dependnecy and offers functions with explicit uniqueness
guarantees. This PR also consolidates fragmented name generation in a
few places to use the new package.

| Old (moby/moby)                     | New                    |
|-------------------------------------|------------------------|
| namesgenerator.GetRandomName(0)     | NameWith("_")          |
| namesgenerator.GetRandomName(>0)    | NameDigitWith("_")     |
| testutil.GetRandomName(t)           | UniqueName()           |
| testutil.GetRandomNameHyphenated(t) | UniqueNameWith("-")    |

namesgenerator package API:
- NameWith(delim): random name, not unique
- NameDigitWith(delim): random name with 1-9 suffix, not unique
- UniqueName(): guaranteed unique via atomic counter
- UniqueNameWith(delim): unique with custom delimiter

Names continue to be docker style `[adjective][delim][surname]`. Unique
names are truncated to 32 characters (preserving the numeric suffix) to
fit common name length limits in Coder.

Related test flakes:
https://github.com/coder/internal/issues/1212
https://github.com/coder/internal/issues/118
https://github.com/coder/internal/issues/1068

codersdk/name.go

@@ -5,8 +5,9 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/moby/moby/pkg/namesgenerator"
 	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/coderd/util/namesgenerator"
 )
 
 var (
@@ -35,7 +36,7 @@ func UsernameFrom(str string) string {
 	if valid := NameValid(str); valid == nil {
 		return str
 	}
-	return strings.ReplaceAll(namesgenerator.GetRandomName(1), "_", "-")
+	return namesgenerator.NameDigitWith("-")
 }
 
 // NameValid returns whether the input string is a valid name.