[8.4](backport #848) Reload downloader client on config change

[mergify]

This is an automatic backport of pull request #848 done by Mergify.
Cherry-pick of 6d830e8 has failed:

On branch mergify/bp/8.4/pr-848
Your branch is up to date with 'origin/8.4'.

You are currently cherry-picking commit 6d830e88d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   internal/pkg/agent/application/managed_mode.go
	modified:   internal/pkg/agent/application/pipeline/emitter/controller.go
	modified:   internal/pkg/agent/application/pipeline/emitter/emitter.go
	modified:   internal/pkg/agent/application/pipeline/router/router.go
	modified:   internal/pkg/agent/application/pipeline/stream/operator_stream.go
	modified:   internal/pkg/agent/operation/operator.go
	modified:   internal/pkg/artifact/download/composed/downloader.go
	modified:   internal/pkg/artifact/download/composed/verifier.go
	modified:   internal/pkg/artifact/download/http/downloader.go
	modified:   internal/pkg/artifact/download/http/verifier.go
	new file:   internal/pkg/artifact/download/reloadable.go
	modified:   internal/pkg/artifact/download/snapshot/downloader.go
	modified:   internal/pkg/artifact/download/snapshot/verifier.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   internal/pkg/agent/application/local_mode.go
	both modified:   internal/pkg/artifact/config.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[elasticmachine]

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• Start Time: 2022-08-05T06:38:29.967+0000

• Duration: 14 min 40 sec

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[michalpristas]

closing in favor of #868