ci(rest): added redoc docs for rest gateway

[deepankarm]

Tested with a workflow in cloud-ops repo: https://github.com/jina-ai/cloud-ops/blob/master/.github/workflows/test-checkout.yml

Run: https://github.com/jina-ai/cloud-ops/runs/1830403348?check_suite_focus=true

Docs with test run: https://api.jina.ai/rest/master.html

[codecov]

Codecov Report

Merging #1860 (f878d0b) into master (5cbe03c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1860   +/-   ##
=======================================
  Coverage   85.92%   85.92%           
=======================================
  Files         146      146           
  Lines        6982     6982           
=======================================
  Hits         5999     5999           
  Misses        983      983           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5cbe03c...14558d0. Read the comment docs.

[github-actions]

Latency summary

Current PR yields:

• 🐎🐎 index QPS at 1108, delta to last 3 avg.: +7%
• 🐢🐢 query QPS at 19, delta to last 3 avg.: -53%

Breakdown

Version	Index QPS	Query QPS
current	1108	19
0.9.28	1093	19
0.9.27	971	61

Backed by latency-tracking. Further commits will update this comment.