Allow mappings & processing on the root stream

[nikita-lavrov]

Summary

Closes https://github.com/elastic/streams-program/issues/265

This PR allows defining new mappings and processing on the root streams, as well as editing the description of the default mappings.

Demo

Screen.Recording.2026-05-19.at.12.36.00.PM.mov

[infra-vault-gh-plugin-prod]

Pinging @elastic/obs-onboarding-team (Team:obs-onboarding)

[kibanamachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: d925092
• Build duration: 49 mins

Failed CI Steps

• FTR Configs #44
• FTR Configs #104

Test Failures

• [job] [logs] FTR Configs #44 / integrations When in the Fleet application and on the Endpoint Integration details page should show the Trusted Apps page when link is clicked

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
datasetQuality	1126	1127	+1
streamsApp	1973	1972	-1
total			-0

Async chunks

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

id	before	after	diff
datasetQuality	541.1KB	541.5KB	+319.0B
streamsApp	2.1MB	2.1MB	-16.4KB
total			-16.1KB

Page load bundle

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

id	before	after	diff
streamsApp	26.4KB	26.4KB	+1.0B

Unknown metric groups

async chunk count

id	before	after	diff
streamsApp	42	40	-2

History

• 💛 Build #450195 was flaky 1100008
• 💛 Build #449355 was flaky e04d863
• 💛 Build #448704 was flaky 93b7249
• 💔 Build #448656 failed aecb47a
• 💛 Build #447850 was flaky 12586ec
• 💛 Build #446696 was flaky 6ee7d94