Bug 1862955 - add (optional) session_id & session_count to Glean client info

[rosahbruno]

Checklist for reviewer:

• Commits should reference a bug or github issue, if relevant (if a bug is referenced, the pull request should include the bug number in the title)
• If adding a new field, the field should have a description (see Bug 1652842 - Add a blocklist field so the environment schema works with pre- and post-bug-1647225 data #576 for an example)
• If coming from a fork, run integration tests: ./.github/push-to-trigger-integration <username>:<branchname>

For glean changes:

• Update templates/include/glean/CHANGELOG.md

For modifications to schemas in restricted namespaces (see CODEOWNERS):

• Follow the change control procedure

[rosahbruno]

@akkomar
Would you be able to review this?

[akkomar]

LGTM. Since I haven't seen the fields that are added here documented in bugs or in the doc, can you re-request the review when mozilla/glean.js#1850 is finalized?

@whd this will add two fields to all Glean tables. Do you want a heads-up before merge?

[whd]

@whd this will add two fields to all Glean tables. Do you want a heads-up before merge?

No unless you want to manually verify the efficacy of this PR in stage without automatically propagating to prod. Scanning history I can't recall being involved in the previous changes to these schemas. I'm mostly interested in PB[ER] changes since those can require an ingestion-sink code update.

[rosahbruno]

@akkomar
The Glean.js PRs have landed and I added the missing CHANGELOG entry that @whd pointed out. This should be ready for review again.

[akkomar]

I have pushed this to a branch in this repo to confirm that all tests are passing: https://app.circleci.com/pipelines/github/mozilla-services/mozilla-pipeline-schemas/3369/workflows/67927c70-749e-4dea-b2c0-712240212177