Environment variables evaluated only at integration runtime

[doru1004]

This patch adds a way to pass environment variables that only get resolved at integration runtime.

These values can be passed as modeline options in this way:

# camel-k: property=camel.component.kafka.brokers={{env:KAFKA_BROKERS}}

This allows images built locally with kamel local create to be deployed in the cloud. If the image depends on any such environment variables, their value needs to be resolved in the deployment script. This ensures that the same modeline option that is provided locally works when run in the cloud environment.

Moreover it provides a safe way to pass sensitive properties such as web hooks. The value of {{env:SLACK_WEBHOOK}} will only become available when the integrations is run. The value will be taken from the parent environment which is either the local machine or a container.

For the case when the parent environment is a container, this patch also adds an --env flag to kamel local run. Previously to run an existing image, it was sufficient to provide the image name:

kamel local run --image <registry>/<image-name>

This still holds if no delayed environment variables are used as modeline options.

If delayed environment variables such as {{env:KAFKA_BROKERS}} are used then the kamel local run command needs to also provide values for these variables:

kamel local run --image <registry>/<image-name> --env KAFKA_BROKERS=localhost:9092

(This is similar to what a docker run command would require)

Release Note

NONE