refactor(ChartDataCommand): separate loading query_context form cache into different module

[ofekisr]

Background

When we have worked on #16991 we wanted to test the new functionalities in concrete and accurate unittest.
All The chartData flows and its components are too couple to superset so it is impossible to create unittests.
The flows are not testable and so many components do not meet the very important principle SRP and the code became so dirty

So I've started to refactor it (#17344 ) but many changes were added and it was hard to review so I decided to split those changes into small PRs so will be easier to follow

This is the third PR in a sequence of PRs to meet these
The next PR is #17407

PR description

The CharaDataCommand responsible is to retrieve data given query context parameters.
What it needs is query_context injected to him so it can fulfill its task. Loading the query_contxt form from the cache is another responsible, thus should be in another module to meet the SRP principle.
The module that is responsible for creating the DataChartCommand and injecting what the command needs, should charge for calling the cache loader.

more small changes:
add "_" prefix to methods name that supposed to be private and remove unused code

Test plans

There are no logic changes, the way the cache is loading is the same as was in the command so new tests are not required

Previous PRs

1. refactor(ChartData): move ChartDataResult enums to common #17399
2. refactor(ChartData): move chart_data_apis from ChartRestApi ChartDataRestApi #17400

[codecov]

Codecov Report

Merging #17405 (c1931b5) into master (28944f5) will increase coverage by 0.01%.
The diff coverage is 95.83%.

@@            Coverage Diff             @@
##           master   #17405      +/-   ##
==========================================
+ Coverage   76.94%   76.96%   +0.01%     
==========================================
  Files        1040     1041       +1     
  Lines       56074    56060      -14     
  Branches     7735     7735              
==========================================
  Hits        43146    43146              
+ Misses      12670    12656      -14     
  Partials      258      258              

Flag	Coverage Δ
hive	81.51% <95.83%> (+0.04%)	⬆️
mysql	81.93% <95.83%> (+0.04%)	⬆️
postgres	81.94% <95.83%> (+0.04%)	⬆️
python	82.29% <95.83%> (+0.04%)	⬆️
sqlite	81.62% <95.83%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/charts/commands/data.py	97.95% <ø> (+1.59%)	⬆️
superset/charts/data/query_context_cache_loader.py	90.00% <90.00%> (ø)
superset/charts/api.py	85.22% <100.00%> (+4.17%)	⬆️
superset/charts/data/api.py	88.48% <100.00%> (+0.25%)	⬆️
...frontend/src/dashboard/components/Header/index.jsx	68.30% <0.00%> (-0.55%)	⬇️

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[amitmiran137]

LGTM!