DDG: Add path agnostic decorations action & reducer

[everett980]

Which problem is this PR solving?

• Lays the groundwork to add "path agnostic" decorations to DDG nodes. For instance: current alert count, or time since last deployment.

Short description of the changes

• Adds action and reducer to fetch data for a given service or operation. Calculates maximum for each decoration to later be used for a color gradient on nodes.

[codecov]

Codecov Report

Merging #549 into master will decrease coverage by 0.01%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##           master     #549      +/-   ##
==========================================
- Coverage   93.00%   92.99%   -0.02%     
==========================================
  Files         197      200       +3     
  Lines        4848     4923      +75     
  Branches     1177     1205      +28     
==========================================
+ Hits         4509     4578      +69     
- Misses        299      305       +6     
  Partials       40       40              

Impacted Files	Coverage Δ
packages/jaeger-ui/src/api/jaeger.js	97.72% <0.00%> (-2.28%)	⬇️
...aeger-ui/src/components/DeepDependencies/index.tsx	99.12% <0.00%> (-0.88%)	⬇️
packages/jaeger-ui/src/model/link-patterns.tsx	93.82% <ø> (-0.62%)	⬇️
packages/jaeger-ui/src/reducers/ddg.tsx	100.00% <ø> (ø)
.../jaeger-ui/src/components/DeepDependencies/url.tsx	97.50% <50.00%> (-2.50%)	⬇️
...aeger-ui/src/actions/path-agnostic-decorations.tsx	100.00% <100.00%> (ø)
...eger-ui/src/reducers/path-agnostic-decorations.tsx	100.00% <100.00%> (ø)
packages/jaeger-ui/src/utils/stringSupplant.tsx	100.00% <100.00%> (ø)
...eViewer/TimelineHeaderRow/TimelineViewingLayer.tsx	88.13% <0.00%> (-5.09%)	⬇️
... and 2 more

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[yurishkuro]

Are there any visuals coming with this PR?

[everett980]

Are there any visuals coming with this PR?

Not in this one. This is just the functionality to fetch and store decoration values (and the max value for each decoration).
Next I'm working on the side bar to select a decoration, as well as display additional information for a selected node.
Then I'm working on node coloring based on the selected decoration.