Submit challenge with poet cert pubkey hint

[ConvallariaMaj]

Motivation

Add cetifier pubkey hint to poet Submit request to support changes on poet service side spacemeshos/poet#501

Description

Pass first 4 bytes of cerifier pubkey as hint for poet + new tests.

Test Plan

• unittests

TODO

• Explain motivation or link existing issue(s)
• Test changes and document test plan
• Update documentation as needed
• Update changelog as needed

[codecov]

Codecov Report

Attention: Patch coverage is 68.75000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 79.8%. Comparing base (516fc47) to head (8302f4c).

Files with missing lines	Patch %	Lines
activation/poet.go	75.0%	2 Missing and 1 partial ⚠️
activation/certifier.go	0.0%	1 Missing ⚠️
sql/localsql/certifier/db.go	66.6%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #6313     +/-   ##
=========================================
- Coverage     79.8%   79.8%   -0.1%     
=========================================
  Files          343     343             
  Lines        44505   44514      +9     
=========================================
- Hits         35548   35546      -2     
- Misses        6952    6970     +18     
+ Partials      2005    1998      -7     

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[poszu]

The change in poet to support extra trusted keys was backward compatible - the poet will accept registrations with certs signed by the main certifier without the hint. Hence, I think this change is not really required.

It would be more interesting to allow loading certificates from disk and using them instead of certifying at the certifier service (then the hint would be required).

[poszu]

It should continue to work the way it was (without passing the hint).

[fasmat]

I don't understand? Sure the node just chose to not provide the certifier pubkey hint and then everything works like before (after the fix in this PR: spacemeshos/poet#523), but if the nodes certificate has been signed by a different Certifier than the one returned from /info of the PoET it is using then it should be able to at least try to still submit in case the PoET accepts certificates from the certifier the node is using or not?

[poszu]

I mean: if the cert is signed by the certifier exposed on info.Certfier.URL, then you don't need to pass the hint (legacy support). If it is not signed by this certifier, then passing info.Certifier.Pubkey makes no sense (as it will be rejected)