[linux] BLE central implementation

[Damian-Nordic]

Problem

Linux platform layer provides functions for the BLE peripheral, however the BLE central role is only partially implemented. As a result, Linux native controllers, such as examples/chip-tool cannot initiate a BLE connection and perform Rendezvous over BLE.
Although examples/chip-tool may get deprecated in the future due to #4334, the changes posted here may still be useful if one needs to implement another controller app, or add the controller capabilities to examples/shell.

Summary of Changes

• For controller applications, configure BLEManagerImpl for Linux as a BLE central device.
• Implement missing functions needed to discover a device with a specific discriminator and automatically connect to it.
• Finish implementation of the BleConnectionDelegate to let the application know that the connection has been established.
• Implement missing pieces needed to communicate over BLE as a BLE central device, such as: sending write request, subscription to a GATT characteristic, indication reception etc.

Fixes #4113, fixes #2791