Enhancement: Implement Agent to manage incoming Bluetooth connections

[Taybenberg]

Details

This PR adds an implementation of the BlueZ pairing Agent and AgentManager.

The Agent implements the org.bluez.Agent1 interface and allows applications
to handle incoming Bluetooth pairing requests (PIN code, passkey, confirmation,
authorization, and service authorization).

The AgentManager provides a wrapper for the org.bluez.AgentManager1 interface
and is used to register, unregister, and optionally set the agent as the
default system agent.

An example project demonstrating how to work with the BlueZ Agent was also added.

All capability modes were tested:

• DisplayOnly
• DisplayYesNo
• KeyboardOnly
• NoInputNoOutput
• KeyboardDisplay

Testing environment:

• Raspberry Pi 3
• Raspberry Pi OS 64-bit (Debian 13 "Trixie")

During testing the following Bluetooth daemon configuration with custom settings
was used (/etc/bluetooth/main.conf):

Class = 0x200414
AlwaysPairable = true
FastConnectable = true
JustWorksRepairing = always
AutoEnable = false

Linked To Issue/Feature

• [Enhancement] Pair with a device requiring an agent with the NoInputNoOutput capability #55 - issue/discussion
• [Enhancement] [vNext] Pairing with pin #34 - issue/discussion

[DamianSuess]

Thank you for the pull request, going to pull it back in give it some tests to see how it goes. Always appreciate seeing good enhancements