TASK-117948: add docs for list-specific suppressions

[rafaelmatsumotomb]

Note

Documents support for list-specific suppressions across the Suppression List API using list_id.

• Adds list_id to the suppression object and updates examples to show list-specific entries
• Extends bulk and single PUT payloads to accept list_id (alphanumeric, hyphens, underscores; omit for account-wide)
• Adds list_id query parameter to search endpoint to filter by mailing list
• Intro text clarifies account-wide vs list-specific suppressions

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