feat(web): Add session handling implementation

[martinkuba]

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Which problem is this PR solving?

Follow up to https://github.com/open-telemetry/opentelemetry-js/pull/4972

Discussed in issue https://github.com/open-telemetry/opentelemetry-js-contrib/issues/2358

Short description of the changes

This adds an implementation of session management for web. It introduces a SessionManager class that is responsible for starting, ending, and persisting sessions.

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• unit tests
• example added to examples/opentelemetry-web

Checklist:

• [x] Followed the style guidelines of this project
• [x] Unit tests have been added
• [ ] Documentation has been updated