[FEAT] Add YAML support for default and custom metrics definition

[Supporterino]

Overview

This pull request introduces the ability to define custom and default metrics for the oracle-db-appdev-monitoring project using YAML files, in addition to the existing TOML format. This enhancement aims to provide users with greater flexibility and familiarity, as YAML is widely used for configuration in many DevOps and cloud-native environments.

Changes

• YAML Parsing: Added support for parsing metric definitions from .yaml and .yml files.
• Unified Loader: Refactored the metric loader to handle both TOML and YAML formats seamlessly.

Usage

Users can now define their metrics in either TOML or YAML format. The application will automatically detect the file type based on the extension and parse accordingly.

Example YAML Metric Definition

metrics:
  - context: "shared_memory_pools"
    metricsdesc:
      size_mb: "Gauge metric with the size of the shared memory pools in megabytes."
      used_mb: "Gauge metric with the used size of the shared memory pools in megabytes."
      free_mb: "Gauge metric with the free size of the shared memory pools in megabytes."
    labels: [pool]
    request: "SELECT pool, ROUND(SUM(bytes) / 1024 / 1024, 2) AS size_mb, ROUND(SUM(CASE WHEN name != 'free memory' THEN bytes ELSE 0 END) / 1024 / 1024, 2) AS used_mb, ROUND(SUM(CASE WHEN name = 'free memory' THEN bytes ELSE 0 END) / 1024 / 1024, 2) AS free_mb FROM v$sgastat WHERE pool IS NOT NULL GROUP BY pool ORDER BY pool"

Backward Compatibility

• Existing TOML files will continue to work without modification.
• No breaking changes to the configuration interface.

---

Closes: #299

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