Simplify bin/report implementation

[Malax]

This PR simplifies the buildpack's metadata collection system by replacing the custom key-value store with a JSON-based metrics system. The intent is to port this to all JVM buildpacks. (See: heroku/heroku-buildpack-java#247)

• Removed the need for manual field categorization and string escaping by leveraging jq for safe output formatting.
• Since we don't need manual field categorization, buildpacks that use heroku/jvm don't have to be kept in sync with metrics changes in heroku/jvm!
• Replaced complex custom YAML generation logic with simple JSON-to-YAML conversion.
• Replaced hardcoded conditional functions with a generic wrapper (_install_conditional_function_wrapper).
• All functions now use the metrics:: namespace

Example

bin/report output with the changes in this PR, no changes from before:

app_has_jdk_overlay: true
openjdk_distribution: "zulu"
openjdk_install_duration: 4.078
openjdk_version: "1.8.0_452"
openjdk_version_selector: "8"

GUS-W-18837218