feat: make token distribution an option

[grumbach]

Description

Summary generated by Reviewpad on 01 Feb 24 09:08 UTC

This pull request contains the following changes:

• The main.rs file adds a new module token_distribution when the feature "distribution" is enabled.

• The Cargo.toml file adds a new feature called distribution, with the value set to ["bitcoin"]. It also modifies the dependency on bitcoin to include optional = true.

• The token_distribution.rs file is a new file added to the sn_faucet/src directory. It includes code for loading and managing the distribution of tokens in the MaidSafe network, defines constants and types, and introduces structs for representing MaidSafe balances and snapshots.

• The faucet_server.rs file underwent several changes, including the addition of #[cfg(feature = "distribution")] attribute to conditionally include code based on the "distribution" feature. It also removes imports, constants, types, and functions, modifies existing functions, and conditional loading of maide_snapshot and maide_pubkeys from the token_distribution module.

If you need further assistance or explanation on any of these changes, please let me know.

[iancoleman]

@joshuef feel free to merge whenever ready, I'll leave the merge button to maidsafers!