Configure all Umami URL dependencies from a config file (mezos tezos-networks, public nodes, graphic proxy, etc.)

Currently we need to re-compile Umami for each new tezos-network available.

This feature request would allow to offload the tezos-net configuration from the code and add it in a configuration file shipped along with the umami-client for default values, but also downloadable from a fixed URL address (at umami-client startup for example).

It currently would need to contain at least all the following :

• Depends of the tezos-network (mainnet, <testnet(s)>, ...):

  • mezos endpoint
  • public-tezos-node endpoint

• Dependencies that does not depend of the tezos-network:

  • graphic-proxy
  • beacon ?
  • ...

Once this mechanism is in place, we could allow :

• default file shipped with umami => we need to perform a release to change it
• include a URL set by default in umami (for example www.umamiwallet.com/umami-stack.json ) => we only need to change this file to publish a new tezos-net endpoint, add or remove a public-node endpoint, etc.
• allow for user-defined value => users can choose to use whatever endpoints they choose => useful for Dev, QA or debugging purposes.

On umami-client startup the checks would be performed in this order :

1. check if user defined value for the file ? if yes, use it (useful for Dev, QA purposes, or if a user ever starts his own full umami-stack)
2. if not, check if URL contains a valid/compatible file ? if yes, use it.
3. if not, check use default embedded values shipped with the umami-client.

If multiple values are present (for example : multiple mainnet umami-stack endpoint, mutliple tezos-node endpoints) : check whether the connectivity is fine and load-balance the usage between them.