Add protect_content global default

[bomzheg]

Description

add global default parameter protect_content for Bot.
Usage. For make all messages by bot protected by default add new keyword arg to Bot constructor:

    bot = Bot(..., protect_content=True, ...)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

I have been using this feaеure in production bot since January 2022, no problems found.

Test Configuration:

• Operating System: Windows 10
• Python version: 3.8

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes