refactor: Organizes the pages in their own folder

[michael-s-molina]

SUMMARY

This PR organizes the pages in their own folder following the discussion outlined here. One of the goals of this change is to standardize page naming and location in the codebase. There was no route changed in this PR.

This work is part of SIP-61

TESTING INSTRUCTIONS

Make sure all routes continue to work as before.

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 #23241 (9ee6012) into master (473a69a) will not change coverage.
The diff coverage is 52.63%.

❗ Current head 9ee6012 differs from pull request most recent head 0ddaf1d. Consider uploading reports for the commit 0ddaf1d to get more accurate results

@@           Coverage Diff           @@
##           master   #23241   +/-   ##
=======================================
  Coverage   67.49%   67.49%           
=======================================
  Files        1906     1906           
  Lines       73414    73414           
  Branches     7958     7958           
=======================================
  Hits        49553    49553           
  Misses      21820    21820           
  Partials     2041     2041           

Flag	Coverage Δ
javascript	53.73% <52.63%> (ø)

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

Impacted Files	Coverage Δ
...erset-frontend/src/pages/AlertReportList/index.tsx	59.64% <ø> (ø)
superset-frontend/src/pages/AllEntities/index.tsx	0.00% <ø> (ø)
...t-frontend/src/pages/AnnotationLayerList/index.tsx	68.05% <ø> (ø)
...perset-frontend/src/pages/AnnotationList/index.tsx	69.35% <ø> (ø)
superset-frontend/src/pages/Chart/index.tsx	0.00% <ø> (ø)
superset-frontend/src/pages/ChartList/index.tsx	55.31% <ø> (ø)
...erset-frontend/src/pages/CssTemplateList/index.tsx	66.66% <ø> (ø)
superset-frontend/src/pages/Dashboard/index.tsx	0.00% <ø> (ø)
...uperset-frontend/src/pages/DashboardList/index.tsx	55.73% <ø> (ø)
superset-frontend/src/pages/DatabaseList/index.tsx	66.01% <ø> (ø)
... and 13 more

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