request: add `hsd.conf` file to `hsd_data`

[pinheadmz]

Purpose: to access the hsd data directory used and maintained by Bob, from other compatible wallets like Palm Reader.

Problem: hsd --prefix ~/.config/Bob/hsd_data also requires --index-tx and --index-address, not to mention the user may have other settings like --no-dns (--api-key may be confusing, maybe only write to file if user has entered an explicit key in Bob's settings)

Suggestion: maintain an up to date hsd.conf file that matches user's current options, so hsd --prefix ~/.config/Bob/hsd_data will open with identical configuration to Bob wallet