esp32_ble_tracker updates for new functionality

[jonofmac]

Added documentation for new features

Description:

Added new feature documentation to the esp32_ble_tracker and added a link to it on the main index

Related issue (if applicable): fixes <Not Applicable>

Pull request in esphome with YAML changes (if applicable): esphome/esphome#3649

Checklist:

• [x] Branch: next is for changes and new documentation that will go public with the next ESPHome release. Fixes, changes and adjustments for the current release should be created against current.
• [x] Link added in /index.rst when creating new documents for new components or cookbook.

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