Defer (certain) parts of setting up snowplow telemetry

What does this MR do?

Defers the more expensive parts of loading snowplow to later in the dom lifecycle.

This will enable us to improve our overall page loading performance.

See #223855 for more context.

Note that Snowplow setup is per instance and needs to be enabled by an administrator https://docs.gitlab.com/ee/development/telemetry/snowplow.html#enabling-snowplow

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

Contributes to #223855