Address top spec-related 404s

[chalin]

This is in support of:

• Post specs update: address 404s and reenabled all checks #3392

Page path and screen class	Views
/docs/specs/otel/trace/semantic_conventions/http/	231
/docs/specs/otel/trace/semantic_conventions/	179
/docs/specs/otel/metrics/semantic_conventions/	157
/docs/specs/otel/trace/semantic_conventions/span-general/	144
/docs/specs/otel/resource/semantic_conventions/	105
/docs/specs/otel/trace/semantic_conventions/messaging/	98
/docs/specs/otel/metrics/semantic_conventions/http-metrics/	59
/docs/specs/otel/trace/semantic_conventions/instrumentation/aws-lambda/	45
/docs/specs/otel/logs/semantic_conventions/events/	35
/docs/specs/otel/resource/semantic_conventions/k8s/	30
/docs/specs/otel/metrics/semantic_conventions/process-metrics/	29
/docs/specs/otel/metrics/semantic_conventions/system-metrics/	28
/docs/specs/otel/metrics/semantic_conventions/hardware-metrics/	23
/docs/specs/otel/metrics/semantic_conventions/runtime-environment-metrics/	23
/docs/specs/otel/trace/semantic_conventions/cloudevents/	23
/docs/specs/otel/trace/semantic_conventions/exceptions/	23
/docs/specs/otel/trace/semantic_conventions/instrumentation/graphql/	21
/docs/specs/otel/trace/semantic_conventions/database/	20
/docs/specs/otel/logs/semantic_conventions/exceptions/	18
/docs/specs/otel/resource/semantic_conventions/host/	18
/docs/specs/otel/trace/semantic_conventions/rpc/	18
/docs/specs/otel/metrics/semantic_conventions/instrumentation/kafka/	16
/docs/specs/otel/resource/semantic_conventions/deployment_environment/	16
/docs/specs/otel/resource/semantic_conventions/process/	16
/docs/specs/otel/resource/semantic_conventions/cloud_provider/aws/ecs/	14
/docs/specs/otel/resource/semantic_conventions/device/	14
/docs/specs/otel/logs/semantic_conventions/	12
/docs/specs/otel/resource/semantic_conventions/cloud_provider/aws/logs/	10

• Add redirect rules for main spec 404s #3410
• ...