[pkg/ottl] Add support for profiles “Link” sub-type

[rockdaboot]

Component(s)

pkg/ottl

Describe the issue you're reporting

Allow accessing the profiles "Link" sub-type

[github-actions]

Pinging code owners:

• pkg/ottl: @TylerHelmuth @evan-bradley @edmocosta

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[axw]

/label -needs-triage waiting-for-code-owners

Makes sense to me, this would for example make it possible to filter out profile samples that have no associated trace span.