[User] Prevent disabled input change by password manager

[nickofthyme]

Summary

Prevents username input from being edited by password manager extensions when disabled.

fixes #204268

Checklist

• [x] Unit or functional tests were updated or added to match the most common scenarios.

[nickofthyme]

@elastic/kibana-security could I get another look at this? Thanks!

[nickofthyme]

Good point @jeramysoucy. Added test in f2ab08d79819974c9c217fd1d00387226fcf5643.

[elasticmachine]

:yellow_heart: Build succeeded, but was flaky

• Buildkite Build
• Commit: 8aba8b44d4a7ca3d541ca3dcfca8a58888e09837

Failed CI Steps

• FTR Configs #70

Test Failures

• [job] [logs] FTR Configs #70 / serverless observability UI Dataset Quality Dataset quality details navigation should go log explorer for degraded docs when the button next to breakdown selector is clicked

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
security	543.3KB	543.3KB	+13.0B

History

• :green_heart: Build #264889 succeeded e36d787a66ddf74e72115ad0783aa87c008bed39
• :green_heart: Build #260602 succeeded f6d7b376182f26e4a205efdc62cf5ab6b364ea79
• :yellow_heart: Build #260457 was flaky c16283e959d13ccc355d54c5f993f86843f2c819

[kibanamachine]

Starting backport for target branches: 8.x

https://github.com/elastic/kibana/actions/runs/12699786102

[kibanamachine]

💚 All backports created successfully

Status	Branch	Result
✅	8.x

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