Implement Event Groups Service Reporting V2Alpha.

[tristanvuong2021]

No description provided.

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This change is 

[riemanli]

Reviewed 2 of 5 files at r1, 2 of 3 files at r2, all commit messages.
Reviewable status: 4 of 5 files reviewed, 1 unresolved discussion (waiting on @tristanvuong2021)

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src/test/kotlin/org/wfanet/measurement/reporting/service/api/v2alpha/EventGroupsServiceTest.kt line 82 at r2 (raw file):

      .thenReturn(
        listEventGroupsResponse {
          eventGroups += listOf(CMMS_EVENT_GROUP, CMMS_EVENT_GROUP)

Why does it return two identical event groups?

[tristanvuong2021]

Reviewable status: 4 of 5 files reviewed, 1 unresolved discussion (waiting on @riemanli)

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src/test/kotlin/org/wfanet/measurement/reporting/service/api/v2alpha/EventGroupsServiceTest.kt line 82 at r2 (raw file):

Previously, riemanli (Rieman) wrote…

Why does it return two identical event groups?

Switched to two different event groups now

[riemanli]

Reviewed 1 of 1 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @Marco-Premier and @stevenwarejones)

[Marco-Premier]

Reviewed 2 of 5 files at r1, 2 of 3 files at r2, 1 of 1 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @tristanvuong2021)