Replace use of sed for yaml templating with Yaml.sh or helm charts

[diverdane]

Is your feature request related to a problem? Please describe.

Several of the scripts in this repo make use of sed to replace templated fields
in YAML files. For example, here's an example field replacement using sed:

```
sed "s#{{ CONJUR_ACCOUNT }}#$CONJUR_ACCOUNT#g"
```

The scripts that use sed for this purpose include:

• 2_admin_load_conjur_policies.sh
• 4_app_create_namespace.sh
• 6_app_build_and_push_containers.sh
• 7_app_deploy.sh

This templating solution is difficult to follow and maintain. It would be better to
replace these uses of sed with either:

• Helm charts wherever possible, e.g. for application deployments and for the Conjur CLI deployment
• Yaml.sh: Refer to https://medium.com/@KarlKFI/yaml-sh-yaml-sans-helm-e983a3dfdaec

Note: this suggestion came up during review for PR #107.

Describe the solution you would like

Helm charts are used wherever possible. Or, for cases such as policy templating, use Yaml.sh.

Describe alternatives you have considered

Additional context

This suggestion came up during review for PR #107.