Add Soroban.RPC.Server and network_passphrase configuration

[miguelnietoa]

Description

Fixes #149

This PR:

1. Add Soroban.RPC.Server struct and receive network_passphrase in Contract functions
2. Deprecate extra_fee_rate parameter which is not necessary due to the addl_resources parameter which will increase Soroban resource fee.

Type of change

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[L-Zuluaga]

Just found some small details, apart from that Looks great! 🚀