feat: [AdsDataManager] add UserListService for creating and managing user lists (#8941)

* feat: add `UserListService` for creating and managing user lists
feat: add `UserListDirectLicenseService` for creating and managing direct user list licenses
feat: add `UserListGlobalLicenseService` for creating and managing global user list licenses
feat: add `MarketingDataInsightsService` for retrieving marketing data insights for a given user list
feat: add `PartnerLinkService` for creating and managing links between advertiser and data partner accounts
feat: add `UserList` resource
feat: add `UserListDirectLicense` resource
feat: add `UserListGlobalLicense` resource
feat: add `UserListGlobalLicenseCustomerInfo` resource
feat: add `PartnerLink` resource
feat: add `UserIdData` to `AudienceMember` to support User ID in audience member ingestion
feat: add `PpidData` to `AudienceMember` to support Publisher Provided ID (PPID) in audience member ingestion
feat: add `IngestUserIdDataStatus` to `IngestAudienceMembersStatus` to report the status of user ID data ingestion
feat: add `IngestPpidDataStatus` to `IngestAudienceMembersStatus` to report the status of PPID data ingestion
feat: add `RemoveUserIdDataStatus` to `RemoveAudienceMembersStatus` to report the status of user ID data removal
feat: add `RemovePpidDataStatus` to `RemoveAudienceMembersStatus` to report the status of PPID data removal
feat: add `GOOGLE_AD_MANAGER_AUDIENCE_LINK` to the `AccountType` enum
feat: add `AgeRange` and `Gender` enums to support demographic breakdown in marketing insights
feat: add new `ErrorReason` values for licensing, user list operations, and permission checks
fix!: changed `conversion_value` field to be optional in message `Event`
docs: add comments to resources and methods to clarify which are available only to data partners
docs: a comment for enum `ErrorReason` is changed to clarify that it is subject to future additions
docs: a comment for field `pair_data` in message `AudienceMember` is changed to clarify it is only available to data partners
docs: a comment for message `PairData` is changed to clarify it is only available to data partners

PiperOrigin-RevId: 873059573

Source-Link: googleapis/googleapis@1e6955c

Source-Link: googleapis/googleapis-gen@91b643a
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