cmd | node: Refactor core flags

[renaynay]

Description

This PR consolidates flags related to adding a core endpoint. The reasoning behind this is to prevent users from having to pass too many flags once #571 is resolved (since the core accessor will now need both a gRPC and RPC endpoint for the celestia-core connection).

New flags

In the case that the default ports are exposed (grpc:9090, rpc:26657) on the celestia-core endpoint:

celestia <node_type> start --core <ip addr of core endpoint>

In the case that custom ports are exposed on the celestia-core endpoint:

celestia <node_type> start --core <ip addr of core endpoint> --core.grpc 9090 --core.rpc 26657

If --core.grpc || --core.rpc are not provided, we assume the defaults and attempt to connect.

[renaynay]

from @YazzyYaz

Immediate thoughts are, it should be explicit:
so --core should mean it’s for the IP address so something like --core.ip
or .grpc and .rpc I’d rather have something like --core.grpc.port and --core.rpc.port since it relates to ports.
my 2 cents (edited)

[codecov-commenter]

Codecov Report

Merging #910 (8ccb595) into main (e0be707) will increase coverage by 0.41%.
The diff coverage is 56.25%.

@@            Coverage Diff             @@
##             main     #910      +/-   ##
==========================================
+ Coverage   58.15%   58.57%   +0.41%     
==========================================
  Files         125      128       +3     
  Lines        7415     7618     +203     
==========================================
+ Hits         4312     4462     +150     
- Misses       2645     2689      +44     
- Partials      458      467       +9     

Impacted Files	Coverage Δ
cmd/flags_core.go	43.10% <33.33%> (-2.55%)	⬇️
node/core/core.go	81.25% <50.00%> (ø)
core/testing.go	78.57% <60.00%> (-4.58%)	⬇️
node/config_opts.go	40.00% <75.00%> (+4.86%)	⬆️
core/client.go	100.00% <100.00%> (ø)
node/components.go	90.36% <100.00%> (+1.17%)	⬆️
node/state/core.go	100.00% <100.00%> (ø)
node/state/state.go	100.00% <100.00%> (ø)
node/testing.go	100.00% <100.00%> (ø)
service/state/core_access.go	21.34% <100.00%> (+1.80%)	⬆️
... and 20 more

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[renaynay]

@YazzyYaz 5192563

[Wondertan]

LGTM, only nits

[liamsi]

LGTM

[adlerjohn]

utACK