add server configuration json

[jakep36]

Allow server configuration so a user running fluree server can manage stuff like open/closed mode, ipfs options, etc.

For GA we'll target at least getting the option to restrict to only requests with credentials allowing server to be run in an open environment without an API in front.

Further options that we may want to add:

• protecting particular ledgers
• allowing create (or delete) for certain identities
• ...

[Jackamus29]

Reference to this ticket was made in Discord:
https://discord.com/channels/896089675511508992/896089675511508995/1258715398723862538

[aaj3f]

This work is at least initially complete by #78

Additional work for closed-mode is described in other tickets, so closing this ticket for now