[Canvas] Versioned and internal routes

[cqliu1]

Summary

Closes #157101.
Closes #157083.

This refactors all Canvas routes to use the versioned router for BWC and makes access for all routes internal only. I also removed the es_fields routes because the last usage of that route was removed in #139610.

All routes have been changed from /api/canvas/* to /internal/canvas/*.

Checklist

Delete any items that are not applicable to this PR.

• 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
• 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

Risk Matrix

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Before closing this PR, invite QA, stakeholders, and other developers to identify risks that should be tested prior to the change/feature release.

When forming the risk matrix, consider some of the following examples and how they may potentially impact the change:

Risk	Probability	Severity	Mitigation/Notes
Multiple Spaces—unexpected behavior in non-default Kibana Space.	Low	High	Integration tests will verify that all features are still supported in non-default Kibana Space and when user switches between spaces.
Multiple nodes—Elasticsearch polling might have race conditions when multiple Kibana nodes are polling for the same tasks.	High	Low	Tasks are idempotent, so executing them multiple times will not result in logical error, but will degrade performance. To test for this case we add plenty of unit tests around this logic and document manual testing procedure.
Code should gracefully handle cases when feature X or plugin Y are disabled.	Medium	High	Unit tests will verify that any feature flag or plugin combination still results in our service operational.
See more potential risk examples

For maintainers

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

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 7b10065

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
canvas	993.2KB	993.4KB	+161.0B

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
canvas	13.3KB	13.3KB	+19.0B

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	13	15	+2
securitySolution	410	414	+4
total			+6

References to deprecated APIs

id	before	after	diff
canvas	134	128	-6

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	14	16	+2
securitySolution	493	497	+4
total			+6

History

• 💔 Build #134955 failed 1a619186121d61798ea03913c72a85fde2c2bf24
• 💔 Build #134142 failed eec087b3feaa602b10aa521df68d445ebde58e5c
• 💔 Build #134137 failed ea2ffd06691389871fa4ebbe7cd1e637ee1e895b

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

[ThomThomson]

Deleted route & versioned router onboarding LGTM, all as expected. Code review only, as it seems to me that if any saved object loading was off in Canvas, many tests would fail!