## Bug description

It appears that merging people doesn't work since #10868, because the shape of a person returned by the persons endpoint turned from `{ ..., "uuid": "00000000-0000-0000-0000-000000000000", "id": 2 }` to `{ ..., "uuid": "00000000-0000-0000-0000-000000000000", "id": "00000000-0000-0000-0000-000000000000" }`. The `/merge` endpoint relies on the serial ID, and now that's not exposed (because this ID isn't even _known_ in ClickHouse).

## How to reproduce

1. Go to a random person.
2. Click "Split or merge IDs"
3. Select some other person(s) to merge into the current person
4. Notice that when you select persons, in the list they appear as some random numbers instead of distinct IDs – that's another symptom of the issue with UUIDs being returned instead of serial IDs.
  <img width="198" alt="Screen Shot 2022-07-28 at 22 24 17" src="https://user-images.githubusercontent.com/4550621/181630574-88b4c029-706a-4134-ac62-a1d0001efd3c.png">
5. Click "Merge persons"
6. See success toast, but realize that actually nothing has happened

## Environment

- [x] PostHog Cloud
- [x] self-hosted PostHog (ClickHouse-based), version/commit: 1.38.0

## Additional context

This was reported by a user [on Slack](https://posthogusers.slack.com/archives/C01GLBKHKQT/p1658810378839129).

#### *Thank you* for your bug report – we love squashing them!

posthog/api/person.py
from posthog.api.documentation import PersonPropertiesSerializer, extend_schema
from posthog.api.routing import PKorUUIDViewSet, StructuredViewSetMixin
from posthog.api.utils import format_paginated_url, get_pk_or_uuid, get_target_entity
from posthog.client import sync_execute
from posthog.constants import (
    CSV_EXPORT_LIMIT,
    INSIGHT_FUNNELS,
    INSIGHT_PATHS,
    LIMIT,
    OFFSET,
    TRENDS_TABLE,
    FunnelVizType,
)
from posthog.decorators import cached_function
from posthog.logging.timing import timed
from posthog.models import Cohort, Filter, Person, User
from posthog.models.activity_logging.activity_log import Change, Detail, Merge, load_activity, log_activity
from posthog.models.activity_logging.activity_page import activity_page_response
from posthog.models.cohort.util import get_all_cohort_ids_by_person_uuid
from posthog.models.filters.path_filter import PathFilter
from posthog.models.filters.retention_filter import RetentionFilter
from posthog.models.filters.stickiness_filter import StickinessFilter
from posthog.models.person.sql import GET_PERSON_PROPERTIES_COUNT
from posthog.models.person.util import delete_ch_distinct_ids, delete_person
from posthog.permissions import ProjectMembershipNecessaryPermissions, TeamMemberAccessPermission
from posthog.queries.actor_base_query import ActorBaseQuery, get_people
from posthog.queries.funnels import ClickhouseFunnelActors, ClickhouseFunnelTrendsActors
from posthog.queries.funnels.funnel_strict_persons import ClickhouseFunnelStrictActors
from posthog.queries.funnels.funnel_unordered_persons import ClickhouseFunnelUnorderedActors
from posthog.queries.paths import PathsActors