Add schema serde utilities

[lovromazgon]

Description

Adds serde (serialization/deserialization) utilities for schemas. Most of the code already existed in conduit and was moved here. Notable changes:

• Introduced the field id on the schema (protobuf and Go type), as it's needed in Conduit to create the Confluent wire format, which has the ID prepended in the header.
  • Note that this is a breaking change for the buf linter, but since that proto file was not released yet we can ignore that.
• A global cache was added for serde objects. The global cache is used so the schema bytes don't have to be parsed every time we process a new record.
• The previous schema.AvroBuilder was moved into the avro package and became avro.Builder.
• This repository contains a stricter linter config, so the code needed to be adjusted in some places (e.g. introduced static error variables, error wrapping, exhaustive switch checks etc.).

Closes #53, closes #51.

Quick checks:

• I have followed the Code Guidelines.
• There is no other pull request for the same update/change.
• I have written unit tests.
• I have made sure that the PR is of reasonable size and can be easily reviewed.

[hariso]

🚀