Allow string-set bootnodes to still work

Signed-off-by: Edward Evans <edward.evans@consensys.net>

templates/config.toml.j2

@@ -94,9 +94,14 @@ permissions-nodes-contract-address="{{ besu_permissions_nodes_contract_address }
 {% endif %}
 
 {% if besu_bootnodes|length > 0 %}
+{% if besu_bootnodes is string %}
+# bootnodes
+bootnodes={{besu_bootnodes}}
+{% else %}
 # bootnodes
 bootnodes=[{{besu_bootnodes|map('to_json')|join(',')}}]
 {% endif %}
+{% endif %}
 
 {% if orion_version is defined %}
 # Orion