Permutive RTD: note params.bidders now triggers ortb2 writes (#6538)

* docs: update permutiveRtdProvider.md for msft bidder custom cohorts

Add msft to supported custom cohort bidders list, document the new
params.bidders configuration, and note the appnexus-to-msft migration path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: align markdown table columns to pass MD060 lint rule

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* remove hardcoded msft default from docs, add publisher config example

Mirrors the code change in Prebid.js PR #14655. The params.bidders
default is now {} and publishers must explicitly configure msft
custom cohort sources.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs(permutiveRtdProvider): note params.bidders now triggers ortb2 writes

Document that listing a bidder under params.bidders causes the module
to write ortb2 for that bidder, even when it is not in acBidders or
Permutive's SSP list. Paired with the Prebid.js fix that iterates
params.bidders keys in setBidderRtb.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* github UI lied to me :P

* how to resolve a simple merge conflict in three commits

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-authored-by: Muki Seiler <muuki88@users.noreply.github.com>