API: New algod endpoint /v2/block/{round}/header omits transactions and cert from response

[nullun]

Retrieve just the block header information without the transactions and cert data. This reduces the response size and response time, but still includes block details such as the proposer and any incentive rewards.

With the introduction of consensus incentives, various people have asked how they can obtain this new data per block without also including all the transaction data in the response. This was considered a useful option, so thought I'd have a go at implementing it. Support for both json and msgpack is available, and a very simple test was included.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.

Project coverage is 56.24%. Comparing base (eff5fb4) to head (c84546f).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
daemon/algod/api/server/v2/handlers.go	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6163      +/-   ##
==========================================
- Coverage   56.29%   56.24%   -0.05%     
==========================================
  Files         494      494              
  Lines       69958    69978      +20     
==========================================
- Hits        39381    39360      -21     
- Misses      27907    27939      +32     
- Partials     2670     2679       +9     

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

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests

[algorandskiy]

Please fix the test, otherwise LGTM

[algorandskiy]

I guess it is better to round trip a header from a mock in the test but LGTM