Define and implement logging strategy for taipy back end code about taipy-core

[jrobinAV]

Strategy:

A TaipyLogger object is available in taipy.core.common.logger.
It holds logger already set with a standard message formatting, such as:

[2022-02-20 17:17:42,504][Taipy][INFO] Loading configuration. Filename: 'my_file.toml'
[2022-02-20 17:17:42,504][Taipy][INFO] Configuration 'my_file.toml' successfully loaded.

By default the minimum log level to display is INFO, but it can be overridden providing a logger config. The path of the file config must be set in an environment variable TAIPY_LOGGER_CONFIG_PATH.

logs:

1. ERROR level

• all the exceptions raised by the execution of a job.
• all the errors returned by the config checker.

2. WARNING level

• No entity is found when trying to get it from an id.
• all the warnings returned by the config checker.
• A data node with no data is read.

3. INFO level

• A file configuration is loaded
• all the infos returned by the config checker.
• A job is completed
• A job is skipped
• A job is forced to be executed

4. DEBUG level

• Each manager/scheduler entry point
• Each Taipy entry point
• The developer's discretion

[florian-vuillemot]

@jrobinAV we should put it in the doc!