[Fleet] Allow to specify an upgrade window for rolling upgrade

[nchaulet]

Summary

Related to #130259

Update the agent upgrade API to allow to specify an upgrade duration in seconds to progressively rollout upgrades

The bulk upgrade now support a new key rollout_duration_seconds

Example:

POST /api/fleet/agents/bulk_upgrade
{
version: 8.2.0,
agents: ['agent1', 'agent2'],
rollout_duration_seconds: 6000,
}

Tests

This is tested with an api integration tests that check we generate the correct .fleet-actions document.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: ab0adda
• Storybooks Preview
• Webpack Bundle Analyzer

Metrics [docs]

Public APIs missing comments

Total count of every public API that lacks a comment. Target amount is 0. Run node scripts/build_api_docs --plugin [yourplugin] --stats comments for more detailed information.

id	before	after	diff
fleet	1266	1269	+3

Unknown metric groups

API count

id	before	after	diff
fleet	1388	1391	+3

History

• 💔 Build #44031 failed ab0ea8d
• 💛 Build #43828 was flaky 6b88b3a

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

cc @nchaulet

[kpollich]

LGTM! Very easy to follow, nice work!