Add support for missing environment variables to SDK

[owais]

State of tracing SDK env var support

• [x] OTEL_RESOURCE_ATTRIBUTES
• [x] OTEL_SERVICE_NAME
• [ ] OTEL_LOG_LEVEL https://github.com/open-telemetry/opentelemetry-python/issues/1059
• [x] OTEL_PROPAGATORS
• [x] OTEL_TRACES_SAMPLER
• [x] OTEL_TRACES_SAMPLER_ARG
• [x] OTEL_BSP_SCHEDULE_DELAY
• [x] OTEL_BSP_EXPORT_TIMEOUT
• [x] OTEL_BSP_MAX_QUEUE_SIZE
• [x] OTEL_BSP_MAX_EXPORT_BATCH_SIZE
• [x] OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT #2051
• [x] OTEL_ATTRIBUTE_COUNT_LIMIT #2055
• [x] OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT #2044
• [x] OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT
• [x] OTEL_SPAN_EVENT_COUNT_LIMIT
• [x] OTEL_SPAN_LINK_COUNT_LIMIT
• [x] OTEL_EVENT_ATTRIBUTE_COUNT_LIMIT #2044
• [x] OTEL_LINK_ATTRIBUTE_COUNT_LIMIT #2044
• [x] OTEL_EXPORTER_JAEGER_AGENT_HOST
• [x] OTEL_EXPORTER_JAEGER_AGENT_PORT
• [x] OTEL_EXPORTER_JAEGER_ENDPOINT
• [x] OTEL_EXPORTER_JAEGER_TIMEOUT
• [x] OTEL_EXPORTER_JAEGER_USER
• [x] OTEL_EXPORTER_JAEGER_PASSWORD
• [x] OTEL_EXPORTER_ZIPKIN_ENDPOINT
• [x] OTEL_EXPORTER_ZIPKIN_TIMEOUT
• [x] OTEL_TRACES_EXPORTER

[AndreasBergmeier6176]

Can you elaborate, why you think OTEL_SERVICE_NAME is implemented? From my experience handling OTEL_SERVICE_NAME at least differs from opentelemetry-golang. The latter sets service.name when Environment Variable is present whereas here it seems like OTEL_SERVICE_NAME is used only in specific cases. Also it seems like the following functionality is missing in Python: https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/commit/227b0dcdc39db4cfc82225b0078a9533aa8cc25a