api: New API with health endpoint

[winder]

Summary

Add a new option for an API which includes a health endpoint to return the current round.

Demo and overview.

Test Plan

New unit tests.

[codecov[bot]]

Codecov Report

Merging #139 (bf2092a) into master (442791a) will increase coverage by 4.05%. Report is 53 commits behind head on master. The diff coverage is 80.81%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
+ Coverage   67.66%   71.71%   +4.05%     
==========================================
  Files          32       37       +5     
  Lines        1976     2747     +771     
==========================================
+ Hits         1337     1970     +633     
- Misses        570      678     +108     
- Partials       69       99      +30     

Files Changed	Coverage Δ
conduit/data/block_export_data.go	100.00% <ø> (+92.30%)	:arrow_up:
conduit/metrics/metrics.go	100.00% <ø> (ø)
conduit/pipeline/metadata.go	69.11% <ø> (ø)
conduit/plugins/config.go	100.00% <ø> (ø)
...duit/plugins/exporters/filewriter/file_exporter.go	81.63% <ø> (-1.06%)	:arrow_down:
conduit/plugins/importers/algod/metrics.go	100.00% <ø> (ø)
...gins/processors/filterprocessor/fields/searcher.go	77.50% <ø> (ø)
...ins/processors/filterprocessor/filter_processor.go	83.82% <ø> (+3.54%)	:arrow_up:
...plugins/processors/filterprocessor/gen/generate.go	34.28% <ø> (ø)
conduit/plugins/processors/noop/noop_processor.go	64.70% <ø> (+6.81%)	:arrow_up:
... and 21 more

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[winder]

LGTM -- do we need to do something special to expose this endpoint in sandbox environments?

A new port would need to be exposed for this to be available in sandbox