Refactor the database metadata to use Protobuf as the serialization protocol

[WenyXu]

What type of enhancement is this?

Refactor, Tech debt reduction

What does the enhancement do?

Currently, our database metadata have following problems:
High level:

• The JSON serialization protocol is not optimal for efficiently storing Vec<u8> data.
• Poor backward compatibility.

Detail:

• TableRoute redundantly stores Peer information multiple times.
• ColumnSchema does not store the SemanticType.

BTW, during the design of the metadata, we should also:

• Consider how to effectively retrieve and cache the metadata.
• Treat structured data as first-class citizens (i.g., Avoid the use of Vec<u8> and HashMap<String, String> as possible).

Implementation challenges

No response