refactor: Refactor and split-up settings

[bgins]

Description

This PR implements the following changes:

• Break up [node.network] settings into smaller groups
• Move [monitoring] settings to [node.monitoring]
• Add defaults.toml with complete settings matching the defaults
• Reduce the settings passed to consumers to the minimum necessary
• Update test fixtures using the new settings
• Update and add comments

A complete version of the updated settings will look something like:

[node]
gc_interval = 1800
shutdown_timeout = 20

[node.database]
url = "homestar.db"
max_pool_size = 100

[node.monitoring]
process_collector_interval = 5000
console_subscriber_port = 6669

[node.network]
events_buffer_len = 1024
poll_cache_interval = 1000

[node.network.ipfs]
host = "127.0.0.1"
port = 5001

[node.network.libp2p]
listen_address = "/ip4/0.0.0.0/tcp/0"
node_addresses = []
announce_addresses = []
transport_connection_timeout = 60
max_connected_peers = 32
max_announce_addresses = 10

[node.network.libp2p.mdns]
enable = true
enable_ipv6 = false
query_interval = 300
ttl = 540

[node.network.libp2p.rendezvous]
enable_client = true
enable_server = false
registration_ttl = 7200
discovery_interval = 600

[node.network.libp2p.pubsub]
enable = false
duplication_cache_time = 1
heartbeat = 60
idle_timeout = 86400
max_transmit_size = 10485760
mesh_n_low = 1
mesh_n_high = 10
mesh_n = 2
mesh_outbound_min = 1

[node.network.libp2p.dht]
p2p_provider_timeout = 30
receipt_quorum = 2
workflow_quorum = 3

[node.network.keypair_config]
random = { }

[node.network.metrics]
port = 4000

[node.network.rpc]
host = "::1"
port = 3030
max_connections = 10
server_timeout = 120

[node.network.webserver]
host = "127.0.0.1"
port = 1337
timeout = 120
websocket_capacity = 2048
websocket_receiver_timeout = 30000

Link to issue

Closes #442

Type of change

• Refactor (non-breaking change that updates existing functionality)
• This change requires a documentation update.
• Comments have been added/updated.

Test plan (required)

All existing tests should pass with the updated fixtures.

[zeeshanlakhani]

Great job @bgins.