script: add script to generate example bitcoin.conf
script: add script to generate example bitcoin.conf

this ensures bitcoind option help is the source of truth and also
gives an example conf file for users to customize and copy to their
data directory.

closes #10746

domob1812/bitcoin,bitcoin/bitcoin,kallewoof/bitcoin,GroestlCoin/bitcoin,fujicoin/fujicoin,sstone/bitcoin,anditto/bitcoin,andreaskern/bitcoin,namecoin/namecore,domob1812/bitcoin,fujicoin/fujicoin,jlopp/statoshi,andreaskern/bitcoin,tecnovert/particl-core,GroestlCoin/GroestlCoin,jlopp/statoshi,ajtowns/bitcoin,fanquake/bitcoin,namecoin/namecoin-core,mruddy/bitcoin,mruddy/bitcoin,GroestlCoin/GroestlCoin,lateminer/bitcoin,anditto/bitcoin,sipsorcery/bitcoin,GroestlCoin/bitcoin,bitcoinsSG/bitcoin,GroestlCoin/GroestlCoin,GroestlCoin/bitcoin,sstone/bitcoin,instagibbs/bitcoin,fanquake/bitcoin,particl/particl-core,lateminer/bitcoin,jamesob/bitcoin,jlopp/statoshi,andreaskern/bitcoin,namecoin/namecore,jambolo/bitcoin,andreaskern/bitcoin,ajtowns/bitcoin,bitcoin/bitcoin,sipsorcery/bitcoin,sipsorcery/bitcoin,sstone/bitcoin,kallewoof/bitcoin,particl/particl-core,fanquake/bitcoin,kallewoof/bitcoin,tecnovert/particl-core,tecnovert/particl-core,bitcoin/bitcoin,anditto/bitcoin,fanquake/bitcoin,namecoin/namecore,fanquake/bitcoin,AkioNak/bitcoin,namecoin/namecoin-core,AkioNak/bitcoin,namecoin/namecoin-core,mruddy/bitcoin,bitcoinsSG/bitcoin,Xekyo/bitcoin,sstone/bitcoin,domob1812/bitcoin,namecoin/namecoin-core,ajtowns/bitcoin,namecoin/namecoin-core,lateminer/bitcoin,Xekyo/bitcoin,instagibbs/bitcoin,jambolo/bitcoin,tecnovert/particl-core,domob1812/bitcoin,GroestlCoin/bitcoin,AkioNak/bitcoin,jamesob/bitcoin,instagibbs/bitcoin,instagibbs/bitcoin,domob1812/bitcoin,jambolo/bitcoin,kallewoof/bitcoin,instagibbs/bitcoin,fujicoin/fujicoin,jambolo/bitcoin,particl/particl-core,andreaskern/bitcoin,Xekyo/bitcoin,sipsorcery/bitcoin,bitcoin/bitcoin,bitcoinsSG/bitcoin,jambolo/bitcoin,bitcoin/bitcoin,fujicoin/fujicoin,AkioNak/bitcoin,jamesob/bitcoin,GroestlCoin/GroestlCoin,sipsorcery/bitcoin,sstone/bitcoin,sstone/bitcoin,Xekyo/bitcoin,fanquake/bitcoin,instagibbs/bitcoin,tecnovert/particl-core,anditto/bitcoin,lateminer/bitcoin,anditto/bitcoin,GroestlCoin/bitcoin,jamesob/bitcoin,jlopp/statoshi,fujicoin/fujicoin,bitcoinsSG/bitcoin,jlopp/statoshi,sipsorcery/bitcoin,namecoin/namecore,GroestlCoin/bitcoin,mruddy/bitcoin,bitcoin/bitcoin,bitcoinsSG/bitcoin,AkioNak/bitcoin,GroestlCoin/GroestlCoin,domob1812/bitcoin,ajtowns/bitcoin,lateminer/bitcoin,particl/particl-core,andreaskern/bitcoin,lateminer/bitcoin,GroestlCoin/GroestlCoin,Xekyo/bitcoin,ajtowns/bitcoin,namecoin/namecore,namecoin/namecoin-core,jamesob/bitcoin,particl/particl-core,mruddy/bitcoin,jamesob/bitcoin,namecoin/namecore,tecnovert/particl-core,jlopp/statoshi,Xekyo/bitcoin,kallewoof/bitcoin,fujicoin/fujicoin,jambolo/bitcoin,kallewoof/bitcoin,AkioNak/bitcoin,particl/particl-core,anditto/bitcoin,mruddy/bitcoin,ajtowns/bitcoin,bitcoinsSG/bitcoin