eatt/l2cap: Add upper tester for L2CAP test cases

This patch adds upper tester for L2CAP ECOC testing e.g.
 - trigger sending data
 - trigger reconfiguration
 - trigger L2CAP ECOC creation as a peripheral
 - initiate ECOC with configurable number of channels
 - configure minimum encryption key size
 - force all profiles to use EATT

Bug: 242033442
Bug: 242032465
Bug: 237399985
Test: PTS Testing
Test: atest BluetoothInstrumentationTests
Tag: #feature

Change-Id: Iee13f61149381dc1adec485bfc6dd216361ad1b9