feat: Create activity instance siren entity

[adkulas]

Creating entity for activity instance.

US158483: Create Activity Instance Siren Object

[github-actions[bot]]

PR Checklist:

Did you use a semver keyword in a commit message?

• [ ] Yes I used one in at least one of my commits
• [ ] No but I will use a semver keyword in the commit message when I merge and squash

Did you paste the Rally US URL in the description?

• [ ] Yes
• [ ] No as there's no corresponding Rally US

[ghost]

:tada: This PR is included in version 2.105.0 :tada:

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

Your semantic-release bot :package::rocket: