[avalanche] Hide the master and session keys in the debug log and console

Summary:
The configuration is printed out to the debug.log/console which can leak the avalanche master key or session key set as options. This diff fixes that:

2022-08-10T19:31:48Z Command-line arg: avamasterkey=****
2022-08-10T19:31:48Z Command-line arg: avasessionkey=****

Test Plan:

./src/bitcoind -avamasterkey=<key> -avasessionkey=<key>

Make sure both keys are obfuscated.

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11839