Restructure deltacat metrics to allow for decorators

[yankevn]

This change restructures deltacat's metrics code to allow for metrics emission via decorator functions. To accomplish this, the MetricsConfigSingleton class is introduced to make the metrics_config object globally available while enforcing immutability as much as possible.

Testing:

• pytest
• Tested on personal stack and verified metrics were created

[yankevn]

Performance test IM results (3 runs each): With changes: [271369, 271709, 260248] Without changes: [278824, 283523, 277561]

If anything this seems to show that the changes are more efficient for whatever reason.

[raghumdani]

Resolved by #294