Send a copy of one Snowplow event to Product Analytics collector

What does this MR do?

• Create a client for the Product Analytics snowplow collector, so that we can send server-side events to it from within GitLab
• Send a copy of one event (issue -> epic promotion) to the Product Analytics collector

Notes:

• The Usage Ping setting is checked before sending events
• The Product Analytics snowplow collector is behind the product_analytics feature flag
• The events will be associated to the self monitoring project
• A future MR will aggregate this event and report it via Usage Ping

Related to #231539 (closed)

Testing instructions

1. Create self monitoring project
2. Enable product_analytics for the project: Feature.enable(:product_analytics, Gitlab::CurrentSettings.self_monitoring_project)
3. Promote an issue to an epic
4. Navigate to the Product Analytics UI within the project
5. Verify that an event is present with the properties "se_category"=>"epics", "se_action"=>"promote", "se_property"=>"issue_id", "se_value"=>{ID} (where {ID} is the ID of the issue that was promoted)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team