API: Block Header API Revamp

[gmalouf]

Summary

The recently added algod endpoint /v2/block/{round}/header has proved problematic for downstream SDK support. This PR:

• Removes that new endpoint entirely (SDK support was not working as-is)
• Adds a new parameter to /v2/block/{round} that allows a client to request the block header without either the certificate or the payset.

Test Plan

A new parameter test case was added to handlers_test.go.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.

Project coverage is 51.77%. Comparing base (c490c22) to head (be04838).

Files with missing lines	Patch %	Lines
daemon/algod/api/server/v2/handlers.go	0.00%	19 Missing ⚠️
...ver/v2/generated/nonparticipating/public/routes.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6248   +/-   ##
=======================================
  Coverage   51.77%   51.77%           
=======================================
  Files         644      644           
  Lines       86523    86511   -12     
=======================================
- Hits        44793    44788    -5     
+ Misses      38863    38855    -8     
- Partials     2867     2868    +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.