Mark Indy wallets as deprecated in 0.9.0

[dbluhm]

The Indy SDK will soon be deprecated in favor of a number of other dependencies, including Aries Askar, Indy CredX, etc. Support for these other components has been included in ACA-Py since 0.7.0 as the "askar" wallet type. A script for migrating from Indy wallets to Askar wallets is available here: https://github.com/hyperledger/aries-acapy-tools.

Given all of the above, it is time to mark usage of Indy wallets as deprecated in ACA-Py as of version 0.9.0. Support for Indy wallets will remain in 0.9.0 but will be removed altogether in a future release. Users of Indy wallets should receive a warning in their agent logs on startup and be encouraged to migrate to Askar as soon as possible.