Add Realtime Viewership API

[leszko]

API Spec

Changes:

• Add api handler for Realtime Viewership API
• Add flags to pass Clickhouse Credentials
• Add Clickhouse Client
• Refactor QuerySpec parsing (to re-use in other APIs)

fix https://linear.app/livepeer/issue/ENG-1652/implement-api-to-deliver-real-time-data

[codecov]

Codecov Report

Attention: Patch coverage is 17.12329% with 121 lines in your changes are missing coverage. Please review.

Project coverage is 28.64721%. Comparing base (1798dc0) to head (9203ba8).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main        #185         +/-   ##
===================================================
- Coverage   28.99628%   28.64721%   -0.34907%     
===================================================
  Files              5           6          +1     
  Lines            269         377        +108     
===================================================
+ Hits              78         108         +30     
- Misses           180         256         +76     
- Partials          11          13          +2     

Files	Coverage Δ
views/query_spec.go	71.42857% <ø> (+71.42857%)	⬆️
views/client.go	19.37984% <35.21127%> (+19.37984%)	⬆️
views/clickhouse.go	0.00000% <0.00000%> (ø)

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Files	Coverage Δ
views/query_spec.go	71.42857% <ø> (+71.42857%)	⬆️
views/client.go	19.37984% <35.21127%> (+19.37984%)	⬆️
views/clickhouse.go	0.00000% <0.00000%> (ø)

[linear]

ENG-1652 Implement API to deliver real-time data

[ecmulli]

I have some comments that need to be addressed but can happen after merging if we need to get this into staging asap.

[victorges]

LGTM either way but made a couple suggestions. The only higher-level issue I have is with the historical metrics being exposed on the same endpoint as the realtime metrics, as I think that can be confusing for using and maintaining this.

[leszko]

@ecmulli @victorges Thanks for all the comments. I addressed most of them. Planning to merge this PR and open the discussion in Discord.