Add Document Contacts bulk create and bulk delete contacts (Preview) (#596)

* Revert "Revert "Document bulk create and bulk delete contacts (Preview) (#577…"

This reverts commit a20990d.

* Document companies and company on bulk contact create and update

Both keys are accepted by POST and PUT /contacts/bulk. They were absent
from the create schema and dropped from the update schema.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Sync bulk contacts examples and error codes with developer-docs

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Document field handling and tag application on bulk contact create

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* Drop the singular company field from bulk contacts

Mirrors intercom/intercom#548259, which removed `company` from the bulk
contacts controller's PERMITTED_FIELDS. The key is now sliced off, so
documenting it would advertise a no-op. Everything it expressed is
already expressible through `companies`, including detach via
`remove: true`.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: VarshSuresh