This is similar to PR #4115 but for LeafNodes.
Compression mode can be set on both side (the accept and in remotes).
```
leafnodes {
port: 7422
compression: s2_best
remotes [
{
url: "nats://host2:74222"
compression: s2_better
}
]
}
```
Possible modes are similar than for routes (described in PR #4115),
except that when not defined we default to `s2_auto`.
Signed-off-by: Ivan Kozlovic <ivan@synadia.com>