[WIP] FlightSQL Ratification based on Community Comments (apache#73)

* Move FlightSql examples to their own subpackage

* Fix checkstyle issues

* fix: change Status use to CallStatus

* Remove unnecessary overhead of wrapping nullable objects into Optionals for the sole purpose of null-checking

* Replace Guava's Preconditions with the ones provided by Apache

* Fix typo in FlightSql.proto

* Fix ordering of schema for FlightSql.proto

* Explain why reserved range of IDs for GetSqlInfo is not entirely in use

* Add comment to CommandGetTables to explain the encoding of table_schema

* Remove redundat information on schemas

* Fixed Javadoc on some methods, added Thread interrupt to executeUpdate methods, and updated Signal exceptions to CallStatus with description

* Replace int32 with uint32 for GetSqlInfo name representation

* Replace AssertionError with StatusRuntimeException for whenever attempting to unpack an invalid protobuf message

* add comment to FlightSql.proto to update_rule and delete_rule

* Replace inconsistent exception handling with CallStatus predetermined exceptions

* correct comment to CreatePreparedStatement on FlightSql.proto

* Remove unused dependencies

* fix: change Status use to CallStatus on FlightSqlProducer

* Changed from if not null check to Objects requireNonNull on Flight SQL Client

* Remove Nullable annotation

* Changed from checkNotNull to Objects#requireNotNull with description on Flight SQL Example

* Add CallOptions to every RPC call by the client

* Fix Maven dependency problems and checkstyle violations

* Replace generic Collections with Lists when order matters in an RPC call

* Fix Javadoc for FlightSqlClient

* Add description to StatusRuntimeExceptions

* Add descriptions to Exceptions

* Correct update_rule and delete_rule description on FlighSql.proto

* Verify wheter Root is empty before sending request to server

* Add call options to PreparedStatement

* Replace constant checking of whether client is open with #checkOpen

* Add CallOptions to #close for PreparedStatement

* Refactor PreparedStatement usages of CallOptions

* Fix broken tests

* Fix FlightSql.proto documentation

* Update documentation for format/FlightSql.proto

Co-authored-by: kylep-dremio <38920967+kylep-dremio@users.noreply.github.com>

* Fix checkstyle violations

* Require non null tables for GetExportedKeys and GetImportedKeys

* Not storing CallOptions in PreparedStatement

* Update documentation comments for protobuf

* Replace IntVector for UInt1Vector for delete_rule and update_rule

* Fix protobuf for FlightSQL

* Fix bug with empty metadata

* Update update_rule and delete_rule documentation on proto

* Remove explicit dependency on JDBC's DatabaseMetaData on UpdateDeleteRules

* Use MessageOptions instead of FieldOptions on proto

* Add missing JavaDoc about 'options' parameter

* Fix CommandGetSqlInfo documentation

* Add @throws to FlightSqlClient#checkOpen JavaDoc

Co-authored-by: Juscelino Junior <juscelinojunior@id.uff.br>
Co-authored-by: Vinicius Fraga <sxvinifp@gmail.com>
Co-authored-by: Rafael Telles <rafael@telles.dev>
Co-authored-by: kylep-dremio <38920967+kylep-dremio@users.noreply.github.com>