[C++] Add C++ single file logger factory

[BewareMyPower]

Motivation

Some users are confused about how to customize the logger in C++ client, while they don't want to build their own cpp library with log4cxx support and change the log4cxx.conf file.

Modifications

• Add a FileLoggerFactory class to support writing logs to a single file.
• Rename the existed SimpleLoggerFactory to ConsoleLoggerFactory to differ it with FileLoggerFactory.
• Use PImpl idiom to hide implementations for these two LoggerFactory classes.
• Add PULSAR_PUBLIC to logger factory classes so that they can be exported.
• Provide an example program that writes logs to a single file.
• Change other examples' topic name to v2 format instead of the old v1 topic format.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage. If you ran the SampleFileLogger program in your local env without any pulsar server, a pulsar-client-cpp.log would be created and it contains the content like following.

Wed May 26 15:34:03 2021 INFO [0x10fde8e00] ConnectionPool:84 Created connection for pulsar://localhost:6650
Wed May 26 15:34:03 2021 ERROR [0x700002a2c000] ClientConnection:422 [<none> -> pulsar://localhost:6650] Failed to establish connection: Connection refused
Wed May 26 15:34:03 2021 INFO [0x700002a2c000] ClientConnection:1446 [<none> -> pulsar://localhost:6650] Connection closed
Wed May 26 15:34:03 2021 ERROR [0x700002a2c000] ClientImpl:181 Error Checking/Getting Partition Metadata while creating producer on persistent://public/default/my-topic -- ConnectError
Wed May 26 15:34:03 2021 INFO [0x700002a2c000] ClientConnection:261 [<none> -> pulsar://localhost:6650] Destroyed connection
Wed May 26 15:34:03 2021 INFO [0x10fde8e00] ClientImpl:483 Closing Pulsar client

[BewareMyPower]

It looks like there's something wrong with the build on CentOS 7, I'll take a look.

[BewareMyPower]

@merlimat Done. PTAL again