Naming consistency: "length" vs "size" vs "bytes" when for payload size

[trask]

Sometimes length is used:

• http.request_content_length
• http.response_content_length

Sometimes size is used:

• message.compressed_size
• message.uncompressed_size
• http.server.request.size (metric)
• http.server.response.size (metric)
• http.client.request.size (metric)
• http.client.response.size (metric)

Sometimes size_bytes is used:

• messaging.message.payload_compressed_size_bytes
• messaging.message.payload_size_bytes

ECS uses bytes

• http.request.body.bytes
• http.response.body.bytes

size makes the most sense to me personally, as bytes seems like it could be the actual bytes.

[lmolkova]

related: #1053

[trask]

it looks like .size is a pretty good option given some existing ECS attributes are using it as well:

• package.size
• file.size
• email.attachments.file.size