Use Dynamic Protocol State API to compute events / metrics

[jordanschalm]

• Replace direct inspection of service events at the FollowerState level with use of the Dynamic Protocol State API.
• Simplifies isFirstBlock function

This addresses the following item from https://github.com/onflow/flow-go/issues/5666:

We still directly operate on service events to emit epoch-related metrics events in the FollowerState (code). We should instead emit metrics events using the Protocol State field, and only manipulate service events with the StateMutator and protocol state machines (lower level logic).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.63636% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 55.52%. Comparing base (20ccd86) to head (c115206). Report is 64 commits behind head on master.

Files	Patch %	Lines
state/protocol/badger/mutator.go	88.63%	4 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5923      +/-   ##
==========================================
- Coverage   55.60%   55.52%   -0.08%     
==========================================
  Files        1127     1028      -99     
  Lines       88833    82582    -6251     
==========================================
- Hits        49398    45857    -3541     
+ Misses      34724    32350    -2374     
+ Partials     4711     4375     -336     

Flag	Coverage Δ
unittests	55.52% <88.63%> (-0.08%)	:arrow_down:

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