internal/cli/server: fix flag behaviour

[manav2401]

This PR achieves the following things

1. When the flag nodiscover was enabled in the old-cli, the node would not discover other peers but still connected to static and trusted peers if required, which was much convenient for our validator and sentry architecture. But, in the new-cli, when we set this flag, we also used to set maxpeers to 0. This would not allow the node to connect to any static peers. Ideally, we've suggested people to use this setting of flags (nodiscover along with maxpeers=0). Now, we can either get rid of this flag and keep the same behaviour in client as it is now by not translating it the new toml file using @pratikpatil024's migration script or we can keep the same behaviour of nodiscover in the client (as geth does). I prefer the latter one.

2. We were unable to send metrics to datadog from some of our internal validator nodes running the new-cli. On investigating further, we found out that in the old-cli, prometheus address was set on based on metrics.addr and metrics.port flags (or pprof.addr and pprof.port flag if the earlier ones are not available). The defaults address in any case is 127.0.0.1:7071. So, ideally even if the users have not provided these flags, the prometheus metrics are exported on the default address. In case of the new-cli, currently we need to explicitly set the address for prometheus. Instead we can set them as default so that the changes on our end (w.r.t to metrics collector) are minimized. Also, if these flags are available, use them to derive prometheus address in the migration script.

3. As finalized in (2), the default port for prometheus is 7071 and with the migration script, we're translating the pprof address + port combination to grpc address. Most of the nodes have pprof port set to 7071 and hence it would not allow prometheus to work. My suggestion is to ignore all pprof flags and just rely on default grpc port which is 3131.

[codecov-commenter]

Codecov Report

Base: 56.84% // Head: 56.83% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (6831a1c) compared to base (77db80c).
Patch coverage: 50.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #529      +/-   ##
===========================================
- Coverage    56.84%   56.83%   -0.01%     
===========================================
  Files          607      607              
  Lines        69996    69997       +1     
===========================================
- Hits         39787    39785       -2     
- Misses       26792    26805      +13     
+ Partials      3417     3407      -10     

Impacted Files	Coverage Δ
internal/cli/server/server.go	30.89% <0.00%> (-0.36%)	⬇️
internal/cli/server/config.go	72.91% <100.00%> (-0.07%)	⬇️
p2p/discover/v4_udp.go	72.75% <0.00%> (-3.19%)	⬇️
les/distributor.go	79.68% <0.00%> (-3.13%)	⬇️
les/utils/limiter.go	90.55% <0.00%> (-1.67%)	⬇️
rpc/client.go	83.72% <0.00%> (-1.17%)	⬇️
p2p/simulations/mocker.go	30.00% <0.00%> (-1.12%)	⬇️
eth/protocols/snap/sync.go	70.30% <0.00%> (-0.98%)	⬇️
les/vflux/server/prioritypool.go	81.25% <0.00%> (-0.94%)	⬇️
p2p/simulations/network.go	57.76% <0.00%> (-0.88%)	⬇️
... and 16 more

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[cffls]

LGTM.