[Minor] Migrate src/plugins/lua/aws_s3.lua to lua_shape

[Minor] Migrate src/plugins/lua/aws_s3.lua to lua_shape

Replace tableshape with lua_shape in AWS S3 plugin.

Changes:
- ts.shape { ... } → T.table({ ... })
- ts.string, ts.boolean, ts.number → T.string(), T.boolean(), T.number()
- ts.number + ts.string / fn → T.one_of({T.number(), T.transform(T.string(), fn)})
- :is_optional() → :optional()
- Added comprehensive documentation to all fields

Schema: settings_schema for AWS S3 configuration including bucket,
region, credentials, timeout, compression, and content options.