[Routing] Adding use of ancillas.

[ammareltigani]

Summarize the task Enable use of ancillas to shorten the shortest path along qubits that need to be adjacent during routing.

Acceptance criteria - when is the task considered done? Once an ancilla allocation strategy is implemented (based on some user-specificed inputs like for e.g. max_number_of_anicllas) and MappingManager is extended by a subclass MappingManagerWithAncillas that enables the adding and removing of ancillary physical qubits to the logical->physical mapping and therefore to the routed circuit.

Related https://docs.google.com/document/d/1df9Onm0Z6ZiU_O7QYRsPtDL1WGTP3330ojEwucI0jZ8/edit#heading=h.3hodzisay0rd

[shawn-peng]

I would like to work on this task.