When the auto-instrumentation attaches to a process using the global
TracerProvider, and there has not been a delegate set, create a span
from the go.opentelemetry.io/auto/sdk package so the OTel Go
auto-instrumentation can instrument the application by default.

Do not allow use of auto/sdk outside of global pkg.

### Added

- Add `Reset` method to `SpanRecorder` in
`go.opentelemetry.io/otel/sdk/trace/tracetest`. (#5994)
- Add `EnabledInstrument` interface in
`go.opentelemetry.io/otel/sdk/metric/internal/x`. This is an
experimental interface that is implemented by synchronous instruments
provided by `go.opentelemetry.io/otel/sdk/metric`. Users can use it to
avoid performing computationally expensive operations when recording
measurements. It does not fall within the scope of the OpenTelemetry Go
versioning and stability [policy](./VERSIONING.md) and it may be changed
in backwards incompatible ways or removed in feature releases. (#6016)

### Changed

- The default global API now supports full auto-instrumentation from the
`go.opentelemetry.io/auto` package. See that package for more
information. (#5920)
- Propagate non-retryable error messages to client in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#5929)
- Propagate non-retryable error messages to client in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`.
(#5929)
- Propagate non-retryable error messages to client in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
(#5929)
- Performance improvements for attribute value `AsStringSlice`,
`AsFloat64Slice`, `AsInt64Slice`, `AsBoolSlice`. (#6011)
- Change `EnabledParameters` to have a `Severity` field instead of a
getter and setter in `go.opentelemetry.io/otel/log`. (#6009)

### Fixed

- Fix inconsistent request body closing in
`go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#5954)
- Fix inconsistent request body closing in
`go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`.
(#5954)
- Fix inconsistent request body closing in
`go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`.
(#5954)
- Fix invalid exemplar keys in
`go.opentelemetry.io/otel/exporters/prometheus`. (#5995)
- Fix attribute value truncation in
`go.opentelemetry.io/otel/sdk/trace`. (#5997)
- Fix attribute value truncation in `go.opentelemetry.io/otel/sdk/log`.
(#6032)