feat(config): Make gRPC http connections configurable

[iamjpotts]

Description:
Make characteristics of the gRPC connections, such as keep alives and timeouts, configurable via ClientBuilder.

• Add a new EndpointConfig struct with configuration values for the tonic Endpoint instances that will be created later
• Add a new endpoint_config method on ClientBuilder to override the default configuration
• Make ClientBuilder public
• Add a new private ManagedNetworkBuilder enum which is accepted by ClientBuilder instead of ManagedNetwork - allowing construction of ManagedNetwork to be delayed until ClientBuilder::build is called, since ManagedNetwork requires EndpointConfig

All of the Client constructor methods now return Result<Self, _> instead of simply Self - this is due to the delayed parsing of the keys of HashMap<String, AccountId> into HostPort, and could be avoided if usage of HashMap<String, AccountId> were replaced with HashMap<HostPort, AccountId> (or HashMap<HostPort, EntityId>).

Related issue(s):

#833
#834

Notes for reviewer:

The node endpoint configuration capability is applicable to any combination of network nodes - both the preconfigured networks (mainnet, testnet, and previewnet), and custom networks. It would be possible, but inconvenient, to add a means to set endpoint configuration on either a Client instance or on one of the Client constructor methods.

Instead, this PR makes ClientBuilder public and adds a method to the builder to override the default endpoint configuration.

Tonic's Endpoint instances are setup when NodeConnection creates a channel:

https://github.com/hashgraph/hedera-sdk-rust/blob/40cc835628347772ca1cc71b9d860e2a4c3b1214/src/client/network/mod.rs#L587-L598

Each NodeConnection is created in either NetworkData::from_addresses or NetworkData::with_address_book

Constructor call sites

NetworkData::from_addresses is typically called during initial creation of a Client via a constructor method on Client

Example: https://github.com/hashgraph/hedera-sdk-rust/blob/40cc835628347772ca1cc71b9d860e2a4c3b1214/src/client/mod.rs#L285-L290

Dynamic network update call sites

NetworkData::with_address_book is a part of the dynamic network update process where a client can periodically alter its preferred choice of nodes, though it can also be called via Client::set_network_from_address_book on a client instance.

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[gsstoykov]

@iamjpotts I've recently taken over with maintaining this SDK. Would like to let you know that all commits require GPG signatures, that is one of the reasons checks are not passing. Will you continue work on this or should I close this PR? I'm happy to support if you decide on continuing the work on this.

[iamjpotts]

@iamjpotts I've recently taken over with maintaining this SDK. Would like to let you know that all commits require GPG signatures, that is one of the reasons checks are not passing. Will you continue work on this or should I close this PR? I'm happy to support if you decide on continuing the work on this.

Leave the pr open in a draft state. I'll close it if I permanently lose interest in it. Its not a priority right now.

The commit was likely unsigned bc I wasn't always signing commits while in draft status.