[Discover] Move state management and data fetching code to new folders

[davismcphee]

Summary

These commits are split out from my working branch for #181963 to make reviewing easier.

Our state management code is currently split between a folder called services and the utils folder. This makes working with the code more difficult, especially where One Discover will soon introduce additional complexity. To make the state management code easier to work with, I moved all of the related files into a single folder called state_management with a utils subfolder for its utility functions.

Similarly, all of our data fetching code was spread between files in the utils folder. For the same reason, I moved these files into a new folder called data_fetching, since they will also undergo a lot of changes for One Discover.

Part of #181963.

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Flaky Test Runner was used on any tests changed
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[davismcphee]

/ci

[davismcphee]

/ci

[davismcphee]

/ci

[davismcphee]

/ci

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[mattkime]

code changes look good and work well. Thanks for breaking apart a larger pr.

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 721630b

Metrics [docs]

✅ unchanged

History

• 💛 Build #207260 was flaky 4b03956
• 💚 Build #206937 succeeded 1872c64322244b1d56364ea95af553b03927675c
• 💔 Build #206782 failed 73cde404c7ab1c96b8f16e0a6c11ddcee3b65d86
• 💔 Build #206781 failed eeeca4d46539adc0614992b1210ad657ae3b2afe
• 💔 Build #206778 failed a80ea0c0147383f9279ce761308193bc95503650

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @davismcphee