[Enhancement] Add code style of protobuf and thrift (StarRocks#18052)

Add code style of protobuf and thrift.

Signed-off-by: imay <buaa.zhaoc@gmail.com>

docs/TOC.md

@@ -599,6 +599,9 @@
   + [TPC-H Benchmark](./benchmarking/TPC-H_Benchmarking.md)
 + Developers
   + [Contribute to StarRocks](./developers/How_to_Contribute.md)
+  + Code Style Guides
+    + [protobuf style guides](./developers/code-style-guides/protobuf-guides.md)
+    + [thrift style guides](./developers/code-style-guides/thrift-guides.md)
   + [Use the debuginfo file for debugging](./developers/debuginfo.md)
   + Development Environment
     + [IDE Setup](./developers/development-environment/ide-setup.md)

docs/developers/code-style-guides/protobuf-guides.md

@@ -0,0 +1,44 @@
+# Rules
+
+## Never use required
+
+As the project involving, any fields may become optional. But if it is defined as required, it can not be removed.
+
+So `required` should not be used.
+
+## Never change the ordinal
+
+To be back compatible, the ordinal of the field SHOULD NOT be changed.
+
+# Naming
+
+## file name
+
+The names of messages are all lowercase, with underscores between words.
+Files should end in `.proto`.
+
+```
+my_message.proto            // Good
+mymessage.proto             // Bad
+my_message.pb                // Bad
+```
+
+## Message Name
+
+Message names start with a capital letter and have a capital letter for each new word, with no underscores, and with `PB` as postfix: MyMessagePB
+
+```protobuf
+message MyMessagePB       // Good
+message MyMessage         // Bad
+message My_Message_PB     // Bad
+message myMessagePB       // Bad
+```
+
+## field name
+
+The names of messages are all lowercase, with underscores between words. 
+
+```
+optional int64 my_field = 3;        // Good
+optional int64 myField = 3;         // Bad
+```

docs/developers/code-style-guides/thrift-guides.md

@@ -0,0 +1,44 @@
+# Rules
+
+## Never use required
+
+As the project involving, any fields may become optional. But if it is defined as required, it can not be removed.
+
+So `required` should not be used.
+
+## Never change the ordinal
+
+To be back compatible, the ordinal of the field SHOULD NOT be changed.
+
+# Naming
+
+## file name
+
+The names of messages are all lowercase, with underscores between words. 
+Files should end in `.thrift`.
+
+```
+my_struct.thrift            // Good
+MyStruct.thrift             // Bad
+my_struct.proto             // Bad
+```
+
+## struct name
+
+Struct names start with a capital letter `T` and have a capital letter for each new word, with no underscores: TMyStruct
+
+```
+struct TMyStruct;           // Good
+struct MyStruct;            // Bad
+struct TMy_Struct;          // Bad
+struct TmyStruct;           // Bad
+```
+
+## field name
+
+The names of struct members are all lowercase, with underscores between words. 
+
+```
+1: optional i64 my_field;       // Good
+1: optional i64 myField;        // Bad
+```