jlcpcb: include board name in gerbers.zip instead of just "gerbers.zip"

[jenda122]

Output of "fab jlcpcb" is named "gerbers.zip" which makes it somewhat difficult when uploading multiple boards to JLC cart.

This changes the default name (unless --nametemplate is specified) to <board_name>-gerbers.zip.

[yaqwsx]

Hi, sorry for the long delay in reviewing. The original idea for gerbers.zip was that you have multiple directories named according to the board, and you want to post-process them automatically; thus, you benefit from having the same name.

However, as I learned myself, this makes your life more complicated when ordering multiple PCBs from JLC. So I would like to change this.

However, I am aware of several usages out there that rely on the naming, so changing this would be a breaking change. Therefore, I would would like to include in a new major release that is planned after an upcoming minor release that adds v7 support.

[jj-uk]

Would it not make more sense to change this so that when a flag is present (e.g. --prefixGerbersWithBoardName), the board name is added, otherwise it defaults to "gerbers.zip" ? That would prevent this from being a breaking change.