Bad merge causes helm AGENT_SECURITY_CONTEXT variable to not get rendered

[bpfoster]

Describe the bug
In PR #3563, we added the ability to configure the traffic agent security context. It looks like in a later commit/merge, the Chart's deployment.yaml was affected, and disturbed the chart logic here. This has since been released into v2.19.0.

You can see that the AGENT_SECURITY_CONTEXT block was moved to inside the if .prometheus.port guard. This is incorrect and will result in the AGENT_SECURITY_CONTEXT block not getting rendered unless we also set prometheus.port.

To Reproduce
Steps to reproduce the behavior:

1. Set agent.securityContext in the helm values
2. Install the traffic manager chart
3. Observe that the traffic manager deployment does not include AGENT_SECURITY_CONTEXT environment variable.

Expected behavior
AGENT_SECURITY_CONTEXT is configured when agent.securityContext helm value is set.

Versions (please complete the following information):

• Output of telepresence version

OSS Client         : v2.19.0
OSS Root Daemon    : v2.19.0
OSS User Daemon    : v2.19.0
OSS Traffic Manager: v2.19.0
Traffic Agent      : docker.io/datawire/tel2:2.19.0

• Operating system of workstation running telepresence commands
  Red Hat Enterprise Linux 8.8
• Kubernetes environment and Version [e.g. Minikube, bare metal, Google Kubernetes Engine]
  kind

VPN-related bugs:
If you're reporting an issue around telepresence connectivity when using a VPN,
and are running Telepresence 2.4.8 or above, please also attach the output
of telepresence test-vpn, and the following information:

• Which VPN client are you using?
• Which VPN server are you using?
• How is your VPN pushing DNS configuration? It may be useful to add the contents of /etc/resolv.conf

Additional context
Add any other context about the problem here.