Add HUB_COMPONENT_DIR implicit variable for deployment hooks

[akranga]

Today we do restrict location where deployment hooks can be found. User will want to interact with artefacts inside component directory. To do so, hubctl should deliver environment variables

• HUB_COMPONENT_DIR - absolute path to component directory
• HUB_BASE_DIR - absolute path to hubfile

This will allow user to write something like pre-deployment hook like

cat << EOF > "$HUB_COMPONENT_DIR/values-generated.yaml"
serviceAccount:
  create: true
  name: "$HUB_COMPONENT"
  automountServiceAccountToken: true
  annotations:
    iam.gke.io/gcp-service-account: "$USER_GSA"
nodeSelector:
  iam.gke.io/gke-metadata-server-enabled: "true"
  kubernetes.io/os: "linux"
EOF

That will seed some additional configuration for helm

[akranga]

Also related to #35 . Proposing a breaking change to use HUB_COMPONENT_DIR as a CWD for hook. Rationale:

• User creates a hook to operate inside component
• If user should source resource inside context of a stack, they should use HUB_BASE_DIR
• If user wants to know hook directory dirname "$0" should do the trick

[akranga]

Also adding extensions to the lookup. This will allow execution of hooks like aws/configure on a stack hook level. So the current script lookup logic is the following:

Resolve script name as:

• find by exact filename
• find by fuzzy logic in probeScriptthat checks for additional prefixes/suffixes such asbin/or.shand_`

Search in directories:

• Component directory
• CWD .
• ./.hub
• ./bin/
• Extensions directory
• System PATH