Introduce Dockerfile with Palladium coin class

Dockerfile

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+FROM lukechilds/electrumx
+
+COPY electrumx-patch/coins_plm.py /electrumx/src/electrumx/lib/coins_plm.py
+
+RUN python3 - <<'PY'
+import re, pathlib
+p = pathlib.Path('/electrumx/src/electrumx/lib/coins.py')
+s = p.read_text(encoding='utf-8')
+
+if 'from electrumx.lib.coins_plm import Palladium' not in s:
+    s += '\nfrom electrumx.lib.coins_plm import Palladium\n'
+
+if '"Palladium": Palladium' not in s:
+    s = re.sub(r'(COIN_CLASSES\s*=\s*\{)', r'\1\n    "Palladium": Palladium,', s)
+
+p.write_text(s, encoding='utf-8')
+print('>> Patched ElectrumX with Palladium coin')
+PY
+
+RUN mkdir -p /certs && \
+    cat >/certs/openssl.cnf <<'EOF' && \
+    openssl req -x509 -nodes -newkey rsa:4096 -days 3650 \
+      -keyout /certs/server.key -out /certs/server.crt \
+      -config /certs/openssl.cnf && \
+    chmod 600 /certs/server.key && chmod 644 /certs/server.crt
+[req]
+distinguished_name = dn
+x509_extensions = v3_req
+prompt = no
+
+[dn]
+C  = IT
+ST = -
+L  = -
+O  = ElectrumX
+CN = plm.local
+
+[v3_req]
+keyUsage         = keyEncipherment, dataEncipherment, digitalSignature
+extendedKeyUsage = serverAuth
+subjectAltName   = @alt_names
+
+[alt_names]
+DNS.1 = plm.local
+IP.1  = 127.0.0.1
+EOF
+
+ENV SSL_CERTFILE=/certs/server.crt
+ENV SSL_KEYFILE=/certs/server.key