Support NODE_NAMES in stellar-core.cfg.tmpl

[gravcat]

One of the nice features in the config file is that you can define NODE_NAMES to give friendly names to keys that can be then referenced later by those friendly names.

example:

NODE_NAMES=[
"GDIQKLQVOCD5UD6MUI5D5PTPVX7WTP5TAPP5OBMOLENBBD5KG434KYQ2  stronghold1",
"GAOO3LWBC4XF6VWRP5ESJ6IBHAISVJMSBTALHOQM2EZG7Q477UWA6L7U  eno",
"GCJCSMSPIWKKPR7WEPIQG63PDF7JGGEENRC33OKVBSPUDIRL6ZZ5M7OO  tempo.eu.com",
"GC5SXLNAM3C4NMGK2PXK4R34B5GNZ47FYQ24ZIBFDFOCU6D4KBN4POAE  satoshipay",
"GD7FVHL2KUTUYNOJFRUUDJPDRO2MAZJ5KP6EBCU6LKXHYGZDUFBNHXQI  umbrel",
"GCGB2S2KGYARPVIA37HYZXVRM2YZUEXA6S33ZU5BUDC6THSB62LZSTYH  sdf_watcher1",
"GCM6QMP3DLRPTAZW2UZPCPX2LF3SXWXKPMP3GKFZBDSF3QZGV2G5QSTK  sdf_watcher2",
"GABMKJM6I25XI4K7U6XWMULOUQIQ27BCTMLS6BYYSOWKTBUXVRJSXHYQ  sdf_watcher3",
]

[QUORUM_SET]
VALIDATORS=[
"$sdf_watcher1", "$sdf_watcher2", "$sdf_watcher3"
]

However, in docker-stellar-core's stellar-core.cfg template, it doesn't do any rendering for a NODE_NAMES value.

Not the end of the world, as I can just put those big long keys in their place to create that list instead, but it would be nice if it was consistent.