cmd: beacon node API timeouts

[gsora]

Add two CLI flags for run:

• --beacon-node-timeout, which allows users to specify a custom HTTP timeout used for beacon node API calls
• --beacon-node-submit-timeout, that allows users to specify a custom HTTP timeout used for submission beacon node API calls, like block and attestation submission.

Both flag default to the previous 2 seconds timeout.

category: feature ticket: none

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 6.66667% with 28 lines in your changes missing coverage. Please review.

Project coverage is 56.68%. Comparing base (82d6f70) to head (b15f7dd).

Files	Patch %	Lines
app/app.go	0.00%	28 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3164 +/- ## ========================================== + Coverage 56.65% 56.68% +0.02% ========================================== Files 208 208 Lines 29202 29216 +14 ========================================== + Hits 16545 16561 +16 Misses 10828 10828 + Partials 1829 1827 -2 ```

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[sonarcloud[bot]]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[gsora]

I'll wait for protocol team's review before merging.

Thanks for your help on the CLI arguments copy!