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:

hedera-sdk-rust/src/client/network/mod.rs

Lines 587 to 598 in 40cc835

	pub(crate) fn channel(&self) -> Channel {
	let channel = self
	.channel
	.get_or_init(|| {
	let addresses = self.addresses.iter().map(|it| {
	Endpoint::from_shared(format!("tcp://{it}"))
	.unwrap()
	.keep_alive_timeout(Duration::from_secs(10))
	.keep_alive_while_idle(true)
	.tcp_keepalive(Some(Duration::from_secs(10)))
	.connect_timeout(Duration::from_secs(10))
	});

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:

hedera-sdk-rust/src/client/mod.rs

Lines 285 to 290 in 40cc835

	pub fn for_network(network: HashMap<String, AccountId>) -> crate::Result<Self> {
	let network =
	ManagedNetwork::new(Network::from_addresses(&network)?, MirrorNetwork::default());
	Ok(ClientBuilder::new(network).disable_network_updating().build())
	}

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.)