Add "features" command to print documentation about all features

[yurishkuro]

Is your feature request related to a problem? Please describe.

Collector has the concept of feature gates. When running the help command one can see (some?) features in the --feature-gates flag, e.g.

--feature-gates flag Comma-delimited list of feature gate identifiers. Prefix with '-' to disable the feature. '+' or no prefix will enable the feature. (default -connector.spanmetrics.legacyMetricNames,-exporter.UsePullingBasedExporterQueueBatcher,-filter.filterlog.useOTTLBridge,-filter.filtermetric.useOTTLBridge,-filter.filterspan.useOTTLBridge,jaeger.sampling.includeDefaultOpStrategies,pkg.translator.prometheus.NormalizeName,-pkg.translator.prometheus.PermissiveLabelSanitization,-processor.tailsamplingprocessor.metricstatcountspanssampled,receiver.jaeger.DisableRemoteSampling,-service.noopTracerProvider,-service.profilesSupport,telemetry.UseLocalHostAsDefaultMetricsAddress,-telemetry.disableAddressFieldForInternalTelemetry,-telemetry.disableHighCardinalityMetrics,telemetry.useOtelWithSDKConfigurationForInternalTelemetry

This output is quite unreadable and does not expose any metadata about individual features.

Describe the solution you'd like

Create a features command that will print a summary of all features and their metadata. The command can optionally accept a specific feature ID to limit the output to just one feature.

Describe alternatives you've considered

There is a way to see the features via zpages extension http://localhost:55679/debug/featurez, but it's not always enabled and is overall a harder way to get to the same info than a CLI command.

opentelemetry-collector/service/internal/graph/host.go

Line 141 in ffcef93

zpages.WriteHTMLFeaturesTable(w, getFeaturesTableData())

[morishima-senpai]

Hi, I would like to work on this:)