Implement P2A component for private ad analytics

[moritzhaller]

Ticket includes:

1. Implement a brave component analogous to P3A to enable private ad analytics
2. Implement dummy question related to ad-confirmations to sanity check reports

Spec:

• https://docs.google.com/document/d/16rNfzPnrdxOghzfnquNVd-YTs8XyWFLn9hEW9s879wM/edit#heading=h.5qffchro4oq9

Related PRs:

• devops resources: https://github.com/brave/devops/pull/3144

[GeetaSarvadnya]

QA Blocked - until the follow-up issue #11552 is fixed

[GeetaSarvadnya]

Removed QA blocked based on #11552 (comment).

The issue can be tested now as the test plan is precise now.

[GeetaSarvadnya]

Verification passed on

Brave | 1.14.72 Chromium: 85.0.4183.83 (Official Build) dev (64-bit)
-- | --
Revision | 94abc2237ae0c9a4cb5f035431c8adfb94324633-refs/branch-heads/4183@{#1658}
OS | Windows 10 OS Version 1903 (Build 18362.1016)

• Verified the test plan from P2A for Brave Ads POC brave-core#5949
• Encountered [Desktop] Follow up of #10081- Implement P2A component for private ad analytics #11552

Verified P2A log for Brave.P2A.ViewConfirmationCount

[3016:9744:0902/232423.349:VERBOSE2:brave_p3a_service.cc(373)] BraveP3AService::OnHistogramChanged: histogram_name = Brave.P2A.ViewConfirmationCount Sample = 2147483646 bucket = 2147483646

Note: P2A host listed in Charles can be tested once issue #11552 is fixed. With the above PR just need to verify logs in the console.

---

Verified passed with

Brave | 1.14.72 Chromium: 85.0.4183.83 (Official Build) dev (64-bit)
-- | --
Revision | 94abc2237ae0c9a4cb5f035431c8adfb94324633-refs/branch-heads/4183@{#1658}
OS | macOS Version 10.14.6 (Build 18G3020)

• Verified test plan from P2A for Brave Ads POC brave-core#5949

• Confirmed the below in my logs:

[11310:775:0902/162917.574843:VERBOSE2:brave_p3a_service.cc(373)] BraveP3AService::OnHistogramChanged: histogram_name = Brave.P2A.ViewConfirmationCount Sample = 2147483646 bucket = 2147483646

Per internal discussions, follow up issues #11552 and #11060 are to be addressed separately.

---

Verification passed on

Brave	1.14.72 Chromium: 85.0.4183.83 (Official Build) dev (64-bit)
Revision	94abc2237ae0c9a4cb5f035431c8adfb94324633-refs/branch-heads/4183@{#1658}
OS	Ubuntu 18.04 LTS

• Verified test plan from P2A for Brave Ads POC brave-core#5949

• Confirmed the below in my logs:

[27034:27034:0903/064548.307601:VERBOSE2:brave_p3a_service.cc(373)] BraveP3AService::OnHistogramChanged: histogram_name = Brave.P2A.ViewConfirmationCount Sample = 2147483646 bucket = 2147483646
'''