Support file-based health checks

[kabicin]

What this PR does / why we need it?:

• Supports file-based health checks by adding a new bool flag .spec.probes.enableFileBased
  • When set to true, the Liberty Deployment/StatefulSet tracks for existence of health check files /output/health/live, /output/health/started and /output/health/ready within the container filesystem to return health statuses for the Pod
  • By default, the directory to check for these files is /output/health but it can be configured using the .spec.probes.fileDirectory field
• Note: I made the decision to use the "default MicroProfile Probes config" (such as common.GetDefaultReadinessProbe()) as the default values for file-based health check configurations when values like periodSeconds are not speciifed. As you know, using file-based health checks requires setting the Exec field to run the startupHealthCheck.sh scripts and others. Normally, in our operators, when Exec != nil, it does not use the "default MicroProfile Probes config" (set via RCO) but instead simply returns the probe itself, meaning it falls back onto K8s defaults.

Does this PR introduce a user-facing change?

• User guide
• CHANGELOG.md

Which issue(s) this PR fixes:

Fixes #