perf: scale sidekiq worker MemoryMax with host memory (#15412)

## Description

This systemd unit is installed on every self-hosted Linux install
(copied by `deployment/setup_18.04.sh` / `setup_20.04.sh`) as well as
our own worker hosts, so the memory cap has to be correct across a wide
range of box sizes.

It is currently a fixed `MemoryMax=1.2G`, chosen when workers ran on 2GB
hosts (#12915). On larger hosts that fixed cap sits at a high fraction
of the limit under normal load, so transient spikes hit the hard limit
and the worker is OOM-restarted more often than necessary (each restart
drops the jobs in-flight at that instant).

Switching to `MemoryMax=60%` makes the cap scale with the host's
physical memory instead of being fixed:

- 2GB host: 60% = 1.2G, identical to today (no regression for small
installs)
- 4GB host: 60% = ~2.4G, room to absorb spikes without a premature
restart
- larger hosts scale proportionally

`MemoryHigh=infinity` is unchanged, so the worker is still never
throttled by cgroup reclaim (kept intentionally since #12871 to avoid
reclaim-induced worker stalls). Only the hard cap changes, and only its
scaling.

Fixes https://linear.app/chatwoot/issue/INF-100

## Type of change

- [x] Performance (non-breaking change which improves performance)

deployment/chatwoot-worker.1.service

@@ -17,7 +17,7 @@ StandardInput=null
 SyslogIdentifier=%p
 LimitNOFILE=65536
 
-MemoryMax=1.2G
+MemoryMax=60%
 MemoryHigh=infinity
 MemorySwapMax=0
 OOMPolicy=stop