1. Remove general receiver and fetcher docs
1. Add more specific menu with docs to help users to find documents easier.

* Remove agent codes and clean up

* fix: Fix MultiScopesAnalysisListener#setPublicAttrs log warn frequently. #6562

1. Rename current STATUS_CODE to HTTP_RESPONSE_STATUS_CODE, real tag key should be http.status_code.
2. Add a new string tag RPC_RESPONSE_STATUS_CODE to hold all string type value tag. The key is `rpc.status_code`.
3. At the backend, keep responseCode for HTTP_RESPONSE_STATUS_CODE tag, but add @Deprecated. Also, add httpResponseStatusCode(a duplicate of responseCode) and rpcStatusCode(for RPC_RESPONSE_STATUS_CODE) fields for OAL.

* Modify `Tags.STATUS_CODE` field name to `Tags.HTTP_RESPONSE_STATUS_CODE` and type from `StringTag` to `IntegerTag`, add `Tags.RPC_RESPONSE_STATUS_CODE` field to hold rpc response code value.

* Add `rpcStatusCode` for `rpc.status_code` tag in the OAL objects. The `responseCode` field is marked as deprecated and replaced by `httpResponseStatusCode` field. 

* Tag `status_code` is still supported in the backend for forward compatbility. Will be removed one year later.
Co-authored-by: 吴晟 Wu Sheng <wu.sheng@foxmail.com>

https://lists.apache.org/thread.html/r4f67a7ed880a493e4e82bd2e9a0c26a6e43c37bbfcdaebe7b1a340dc%40%3Cdev.skywalking.apache.org%3E

Co-authored-by: 吴晟 Wu Sheng <wu.sheng@foxmail.com>