Add attributes request/response body size for rpc

[crossoverJie]

Ref: https://github.com/open-telemetry/opentelemetry-java-instrumentation/pull/11833#discussion_r1689747737

Changes

Add attributes:

• rpc.client.request.body.size
• rpc.client.response.body.size
• rpc.server.request.body.size
• rpc.server.response.body.size

Merge requirement checklist

• [x] CONTRIBUTING.md guidelines followed.
• [x] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [x] schema-next.yaml updated with changes to existing conventions.

[crossoverJie]

@trask @lmolkova Please take a look.

[github-actions[bot]]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[crossoverJie]

Any updates?