config: add comments, remove koanf tag, fix toml Duration

[jchappelow]

This change adds "comment" tags, which are used in two places:

• TOML comments for each field or section
• cli flag descriptions

This also removes the unneeded "koanf" tags and now specify "toml" as the attribute tag used for config merging.

Replace a few time.Duration fields with config.Duration so these durations are set correctly as duration strings in TOML rather than giant integers.

Finally, remove the replaces from go.mod and go mod tidy.

kwild print-config example output:

# log level
# possible values are 'debug', 'info', 'warn', and 'error'
log_level = 'info'
# log format
# possible values are 'json', 'text' (kv), and 'plain' (fmt-style)
log_format = 'plain'
# private key to use for node
privkey = 'a4071a2debdd8c31f19cee9642586b9196af6cc236a11f39445d5123d82079eb'

# P2P related configuration
[p2p]
# IP address to listen on for P2P connections
ip = '127.0.0.1'
# port to listen on for P2P connections
port = 6601
# enable peer exchange
pex = true
# bootnodes to connect to on startup
bootnodes = ['0226b3ff29216dac187cea393f8af685ad419ac9644e55dce83d145c8b1af213bd#0@127.0.0.1:6600']

# Consensus related configuration
[consensus]
# timeout for proposing a block (applies to leader)
propose_timeout = '1s'
# max size of a block in bytes
max_block_size = 50000000
# max number of transactions per block
max_txs_per_block = 20000

# DB (PostgreSQL) related configuration
[db]
# postgres host name (IP or UNIX socket path)
host = '127.0.0.1'
# postgres TCP port (leave empty for UNIX socket)
port = '5433'
# postgres role/user name
user = 'kwild'
# postgres password if required for the user and host
pass = ''
# postgres database name
dbname = 'kwild'
# timeout on read transactions from user RPC calls and queries
read_timeout = '45s'
# maximum number of DB connections to permit
max_connections = 60

# User RPC service configuration
[rpc]
# address in host:port format on which the RPC server will listen
listen = '0.0.0.0:8485'
# user request duration limit after which it is cancelled
timeout = '20s'
# largest permissible user request size
max_req_size = 6000000
# enable private mode that requires challenge authentication for each call
private = false
# lifetime of a server-generated challenge
challenge_expiry = '30s'
# maximum number of challenges per second that a user can request
challenge_rate_limit = 10.0

# Admin RPC service configuration
[admin]
# enable the admin RPC service
enable = true
# address in host:port format or UNIX socket path on which the admin RPC server will listen
listen = '127.0.0.1:8585'
# optional password for the admin service
pass = ''
# disable TLS when the listen address is not a loopback IP or UNIX socket
notls = false
# TLS certificate for use with a non-loopback listen address when notls is not true
cert = 'admin.cert'
# TLS key for use with a non-loopback listen address when notls is not true
key = 'admin.key'

# Snapshot creation and provider configuration
[snapshots]
# enable creating and providing snapshots for peers using statesync
enable = false
# snapshot creation period in blocks
recurring_height = 14400
# number of snapshots to keep, after the oldest is removed when creating a new one
max_snapshots = 3

# Statesync configuration (vs block sync)
[state_sync]
# enable using statesync rather than blocksync
enable = false
# trusted snapshot providers in node ID format (see bootnodes)
trusted_providers = []
# how long to discover snapshots before selecting one to use
discovery_time = '30s'
# how many times to try after failing to apply a snapshot before switching to blocksync
max_retries = 3