Variable paymentservice error rate and introduce loyalty level attributes

[rcastley]

Changes

Introduced an enhancement to the feature flag paymentServiceFailure:

• Selectable error rate percentage in the Flagd UI
• app.loyalty.level also added as a span attribute. Gold will show errors when feature flag set.
• Changed pino to include the service.name in log entries and also change from numeric level to text level e.g. info, warn etc.

This makes for a more interesting use case when the payment service fails. Only the gold loyalty level will show errors, all other levels will show success.

Merge Requirements

For new features contributions, please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[julianocosta89]

Hello @rcastley 👋🏽

Thanks for suggesting this.
I'd change a bit the approach though. Instead of having 75% set on the code, ideally we would configure this directly on the Feature Flag, using fractional evaluation: https://openfeature.dev/specification/glossary/#fractional-evaluation
Imagine a slider, where we select the % of failure we want to have.

Hardcoding 75% will create some unexpected behaviour.

[julianocosta89]

LGTM, Just a typo that needs fix, but should be good to go! 🚀

[puckpuck]

Thank you @rcastley this is great!