This gem provides a minimal Railtie to use in lieu of manual configuration.

Operators may customize SDK settings using environment variables but this gem will provide some defaults:

Sets a minimal set of values for OTEL_SERVICE_NAME and OTEL_RESOURCE_ATTRIBUTES when left unset
Users may override SDK configurations using standard OTel SDK environment variables
Users may override Instrumentation libraries are configurable using OTEL_RUBY_*_CONFIG_OPTS

This commit moves the Railtie from its own gem into opentelemetry-instrumentation-rails.

Users will have to explicitly require the railtie in their bundler file or as part of Rails bootstrap after bundler
has required dependencies.

It also reverses the decision to set default OTEL_RESOURCES_ATTRIBUTES based on the Rails.env since we have run into
some issues in production.

cc: @robertlaurin @ericmustin