Make Headers Setter extension context default value configurable

[kyo-ke]

Component(s)

No response

Is your feature request related to a problem? Please describe.

We are pushing traces to Tempo via opentelemetry collector.
when we push trace to multitenant Tempo we need to handle X-Scope-OrgID header using Headers Setter extension.
in current version if user do not specify X-Scope-OrgID this extension automatically use "" as value.(Default value is hardcoded)
and sometimes we want to use specific tenant to store user's trace with no X-Scope-OrgID

problem is we cannot configure default value when specified key is missing.
(https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/extension/headerssetterextension/internal/source/context.go#L24)

Describe the solution you'd like

Make default value configurable for Headers Setter extension's context functionality.
we will create PR for this.

Describe alternatives you've considered

No response

Additional context

No response

[crobert-1]

Hello @kyo-ke, thanks for filing this issue! Is this the same problem as reported in #34412? If so, it would be preferable to only have one issue open for a given issue, but let me know if I'm missing something here 👍

[github-actions]

Pinging code owners for extension/headerssetter: @jpkrohling. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[kyo-ke]

Hello @crobert-1
Thank you for quick response!
yes this is same with #34412.
will close this issue.
I created PR for this. Is it ok to keep my PR open with changing issue number in changelog?

[crobert-1]

Thanks @kyo-ke!

Closing in favor of #34412