WIP: implement server for rendering diff

[iOliverNguyen]

This PR supports 2 formats for render URL, which allows responding combined data for rendering diff:

format: single

• URL: /render?from=...&until=...
• Response:
  • add "format": "single" to flamebearer and metadata
  • levels: x_offset, total, self, name_index

{
  "flamebearer": {
    "format": "single",
    "names": [ ... ]
    "levels": [ i, ..., i+3 ]
    // ....
  },
  "metadata": {
    "format": "single",
    // ....
  },
  "timeline": { ... }
}

format: double

• URL: /render?left=...&until=...&leftFrom=...&leftUntil=...&rightFrom=...&rightUntil=...
• Response:
  • add "format": "double" to flamebearer and metadata
  • levels: left_x_offset, left_total, left_self, right_x_offset, right_total, right_self, name_index

{
  "flamebearer": {
    "format": "double",
    "names": [ ... ]
    "levels": [ i, ..., i+6 ]
    // ...
  },
  "metadata": {
    "format": "double",
     // ...
  },
  "timeline": { ... }
}

Depends: #288

[codecov]

Codecov Report

Merging #290 (bd2230c) into main (9327bd6) will increase coverage by 1.13%.
The diff coverage is 81.09%.

@@            Coverage Diff             @@
##             main     #290      +/-   ##
==========================================
+ Coverage   53.16%   54.29%   +1.13%     
==========================================
  Files          96       97       +1     
  Lines        4244     4421     +177     
==========================================
+ Hits         2256     2400     +144     
- Misses       1773     1802      +29     
- Partials      215      219       +4     

Impacted Files	Coverage Δ
pkg/server/handler.go	0.44% <0.00%> (-<0.01%)	⬇️
pkg/server/render.go	55.79% <30.24%> (-22.39%)	⬇️
pkg/storage/tree/treediff.go	98.51% <98.51%> (ø)
pkg/storage/tree/flamebearer.go	100.00% <100.00%> (ø)
pkg/agent/target/target.go	54.29% <0.00%> (ø)

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[iOliverNguyen]

Also, I'm working on combining data from 2 trees into the new flamebearer format: [i+0, ..., i+6].

[petethepig]

Closed this one as all the commits are copied in #289