fix: should update last_modified_time in client-side after save dash

[graceguo-supercat]

SUMMARY

This PR is to fix an issue related to #11220 . To reproduce:

1. open a dashboard and edit,
2. save change, successfully,
3. in the same browser window, edit same dashboard again,
4. when you try to save the 2nd change, you will see error message.

The root cause is, after user's first update, the client-side still hold the previous value for dashboard last_updated_time. On user submit the second edit, server-side compare the last_updated_time with newer one and will reject the 2nd edit request.

This PR adds solution for this issue: update last_updated_time in client-side when the first save is successful.

TEST PLAN

CI and new unit test.

ADDITIONAL INFORMATION

• Has associated issue: feat: prevent co-edit dashboard collision #11220

[ktmud]

This thing is getting a little too bloated. I'm wondering whether we can refactor and just pass a dashboard object to this component.

[graceguo-supercat]

yes. dashboardInfo is read only dashboard metadata. I will consider group other edit-able dashboard metadata into another object.

[codecov-io]

Codecov Report

Merging #11305 into master will decrease coverage by 1.33%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #11305      +/-   ##
==========================================
- Coverage   62.71%   61.38%   -1.34%     
==========================================
  Files         441      834     +393     
  Lines       14721    39562   +24841     
  Branches     3610     3610              
==========================================
+ Hits         9233    24286   +15053     
- Misses       5307    15095    +9788     
  Partials      181      181              

Flag	Coverage Δ
#javascript	62.71% <ø> (ø)
#python	60.59% <ø> (?)

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

Impacted Files	Coverage Δ
...erset-frontend/src/dashboard/components/Header.jsx	35.65% <ø> (ø)
...src/dashboard/components/HeaderActionsDropdown.jsx	62.22% <ø> (ø)
...et-frontend/src/dashboard/components/SaveModal.jsx	40.90% <ø> (ø)
...ntend/src/dashboard/containers/DashboardHeader.jsx	100.00% <ø> (ø)
...-frontend/src/dashboard/reducers/dashboardState.js	74.54% <ø> (ø)
...frontend/src/dashboard/reducers/getInitialState.js	0.00% <ø> (ø)
superset/utils/dashboard_import_export.py	60.71% <0.00%> (ø)
superset/views/filters.py	100.00% <0.00%> (ø)
...et/migrations/versions/12d55656cbca_is_featured.py	0.00% <0.00%> (ø)
superset/examples/birth_names.py	97.59% <0.00%> (ø)
... and 389 more

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