refactor: reduce and simplify usage of getEnv()

[danstarns]

• performance: high latency when using otel libs inside common endpoints #4741

In most of the exporters, there is a function getEnv() that is called an unnecessary amount of times inside nested ternary operators.

It looks as getEnv() calls parseEnvironment() that happens to iterate over a large static object parsing its values and performing other assertions.

See extract from source:

• https://github.com/open-telemetry/opentelemetry-js/blob/main/experimental/packages/exporter-trace-otlp-http/src/platform/node/OTLPTraceExporter.ts#L57

  getDefaultUrl(config: OTLPExporterNodeConfigBase): string {
    return typeof config.url === 'string'
      ? config.url
      : getEnv().OTEL_EXPORTER_OTLP_TRACES_ENDPOINT.length > 0
      ? appendRootPathToUrlIfNeeded(getEnv().OTEL_EXPORTER_OTLP_TRACES_ENDPOINT)
      : getEnv().OTEL_EXPORTER_OTLP_ENDPOINT.length > 0
      ? appendResourcePathToUrl(
          getEnv().OTEL_EXPORTER_OTLP_ENDPOINT,
          DEFAULT_COLLECTOR_RESOURCE_PATH
        )
      : DEFAULT_COLLECTOR_URL;
  }

This PR reduces the total invocations of getEnv along the exporters in the hope of easing performance and readability.

[pichlermarc]

Thanks. This is more readable now 👍

FYI performance-wise this would not change a lot since all the changed functions are not called on a hot path (only once on start-up).

[pichlermarc]

Please also add a changelog entry to the unrelased section, subsection enhancement in CHANGELOG.md and experimental/CHANGELOG.md then we can merge this. 🙂

[danstarns]

Please also add a changelog entry to the unrelased section, subsection enhancement in CHANGELOG.md and experimental/CHANGELOG.md then we can merge this. 🙂

Updated @pichlermarc 👍