use the term "AnonCreds" rather than Indy

[TimoGlastra]

Based on comment from @swcurran he proposes to move away from the term indy and start using the term AnonCreds. Question is whether it's worth to do a migration over this, and whether we want to all at once or start using the new term for new features/code (could be confusing I guess)

https://github.com/hyperledger/aries-framework-javascript/issues/737#issuecomment-1117724641