add api support for abci streaming to external systems

[egaxhaj]

Description

Adds support for streaming BeginBlocker and EndBlocker request and responses to external systems.

closes: #940

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #952 (7ddd870) into main (77b5e42) will decrease coverage by 0.02%.
The diff coverage is 46.77%.

@@            Coverage Diff             @@
##             main     #952      +/-   ##
==========================================
- Coverage   56.79%   56.76%   -0.03%     
==========================================
  Files         181      182       +1     
  Lines       22273    22333      +60     
==========================================
+ Hits        12649    12678      +29     
- Misses       8651     8677      +26     
- Partials      973      978       +5     

Impacted Files	Coverage Δ
app/app.go	84.55% <22.22%> (-2.57%)	⬇️
app/streaming/trace/service/service.go	65.71% <65.71%> (ø)

[derekadams]

LGTM

[SpicyLemon]

This needs unit/integration tests.

I'm also unsure what the difference between this stuff and the plugins stuff is. An actual use case and some unit tests would probably help with that respect though.

[SpicyLemon]

Just a couple more small things.

[arnabmitra]

i think this PR looks good to me, the "omitted" use case i am not sure i understand but it being controlled by the flag makes it sound code wise..

[egaxhaj]

closing this for now in favor of a grpc approach discussed here. Will keep the repo open for reference.