floss: Support adding/removing/clearing GATT Services in btclient

Support the ability to add, remove, and clear GATT Service on a GATT
Server via btclient.

Bug: 323943663
Test: m -j && manually with btclient
Flag: Exempt, Floss-only change

Change-Id: I355be197e1467106194d28a2749c1335c197e7f9