chore: Feature flag for embedding charts

[geido]

SUMMARY

Users of Superset might not want to give the ability to embed charts, especially as embedding uses iFrames that might be disabled for security reasons. This PR adds a EMBEDDABLE_CHARTS flag to the config to enable/disable embedding charts. Default to True.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

Set the feature flag off and make sure the Embed code option isn't appearing as a Share option in Explore.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #20804 (855318b) into master (922b4b8) will increase coverage by 0.04%.
The diff coverage is 95.95%.

❗ Current head 855318b differs from pull request most recent head bffa407. Consider uploading reports for the commit bffa407 to get more accurate results

@@            Coverage Diff             @@
##           master   #20804      +/-   ##
==========================================
+ Coverage   66.29%   66.34%   +0.04%     
==========================================
  Files        1758     1756       -2     
  Lines       66801    66749      -52     
  Branches     7055     7060       +5     
==========================================
- Hits        44288    44284       -4     
+ Misses      20713    20667      -46     
+ Partials     1800     1798       -2     

Flag	Coverage Δ
javascript	51.98% <94.44%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
...ackages/superset-ui-core/src/query/types/Column.ts	100.00% <ø> (ø)
...ackages/superset-ui-core/src/utils/featureFlags.ts	100.00% <ø> (ø)
.../plugin-chart-echarts/src/MixedTimeseries/index.ts	25.00% <ø> (ø)
...ols/DndColumnSelectControl/ColumnSelectPopover.tsx	3.75% <0.00%> (ø)
...tend/src/explore/components/controls/ViewQuery.tsx	72.72% <ø> (ø)
superset/config.py	91.47% <ø> (ø)
superset/views/core.py	75.64% <50.00%> (-0.04%)	⬇️
superset/views/datasource/utils.py	95.34% <95.34%> (ø)
...et-ui-chart-controls/src/components/labelUtils.tsx	100.00% <100.00%> (ø)
...perset-ui-core/src/chart/components/SuperChart.tsx	100.00% <100.00%> (ø)
... and 13 more

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[zhaoyongjie]

LGTM

[geido]

/testenv up FEATURE_EMBEDDABLE_CHARTS=false

[github-actions]

@geido Ephemeral environment spinning up at http://34.214.222.137:8080. Credentials are admin/admin. Please allow several minutes for bootstrapping and startup.

[github-actions]

Ephemeral environment shutdown and build artifacts deleted.