Nomad v1.0.0 introduced a regression where the client configurations
for `connect.sidecar_image` and `connect.gateway_image` would be
ignored despite being set. This PR restores that functionality.
There was a missing layer of interpolation that needs to occur for
these parameters. Since Nomad 1.0 now supports dynamic envoy versioning
through the ${NOMAD_envoy_version} psuedo variable, we basically need
to first interpolate
${connect.sidecar_image} => envoyproxy/envoy:v${NOMAD_envoy_version}
then use Consul at runtime to resolve to a real image, e.g.
envoyproxy/envoy:v${NOMAD_envoy_version} => envoyproxy/envoy:v1.16.0
Of course, if the version of Consul is too old to provide an envoy
version preference, we then need to know to fallback to the old
version of envoy that we used before.
envoyproxy/envoy:v${NOMAD_envoy_version} => envoyproxy/envoy:v1.11.2@sha256:a7769160c9c1a55bb8d07a3b71ce5d64f72b1f665f10d81aa1581bc3cf850d09
Beyond that, we also need to continue to support jobs that set the
sidecar task themselves, e.g.
sidecar_task { config { image: "custom/envoy" } }
which itself could include teh pseudo envoy version variable.
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