fix(tabconf7): use just cli on _init_regtest_sp to communicate with bitcoind regtest

The changes 098edf7 introduced a bug
and uncovered the real issue behind the `_init_regtest_sp` command.

Up to that commit the initialization was using the output from the
signet chain set up inside the nix environment. As the environment was
built ensuring signet was running, the issue was not evident, until
someone tried using it outside of the nix environment.

The 098edf7 changes assumed the command
was just referring to the wrong blockchain, and applied a fix along
these lines. This change later uncovered other issues.

The simplest fix is to use the agnostic `just cli` recipe, that only
knows about the regtest ports and uses the credentials set up during
initialization.

Author: nymius

doc/tabconf7/justfile

@@ -483,7 +483,7 @@ _init_regtest_sp:
   #!/usr/bin/env bash
   if [ ! -f ".regtest_tr_xprv" ]; then
     rm -rf ".sp_cli2_regtest.db"
-    BLOCKCHAININFO=$(bitcoin-cli --datadir=$BITCOIN_DATA_DIR --chain=regtest getblockchaininfo)
+    BLOCKCHAININFO=$(just cli getblockchaininfo)
     HEIGHT=$(echo $BLOCKCHAININFO | jq -r '.blocks')
     HASH=$(echo $BLOCKCHAININFO | jq -r '.bestblockhash')
     DB_PATH=".sp_cli2_regtest.db" sp-cli2 create --network regtest --birthday-height $HEIGHT --birthday-hash $HASH | jq -r '.tr_xprv' > ".regtest_tr_xprv"