Add BT GATT client and bt fixes

[ferdy-lw]

Submission Checklist 📝

• I have updated existing examples or added new ones (if applicable).
• I have used cargo fmt command to ensure that all changed code is formatted correctly.
• I have used cargo clippy command to ensure that all changed code passes latest Clippy nightly lints.
• My changes were added to the CHANGELOG.md in the proper section.

Pull Request Details 📖

Add bluedroid BT GATT client, gap methods for resolving advertising data, and fix gap setting security params

Description

• Added bluedroid gatt client
• Added example for using the gatt client that connects to the gatt server example
• Added gap method to extract advertising data
• Updated gap scan result to use a struct, and associated enums, instead of wrapping the esp type
• Fix errors in gap not setting the security params correctly, and not setting the auth method
• Fix the gatt server example where clients could not reconnect after the first connection
• Fix the gatt server example to actually support subscribe/unsubscribe via writing to the CCCD descriptor

Testing

Added an example client bt_gatt_client, and I use this client in some of my own projects (victron inverter control)

[ivmarkov]

Most important change is the request to get rid of the heapless dependency in the public API.

The rest is really minimal stuff which should be very easy to fix.