L2 Constructs for AWS Elemental MediaPackageV2

## Description

Adding L2 constructs for AWS Elemental MediaPackageV2 to help with simplifying the developer experience required in L1's today.
We will greatly simplify the developer experience in CDK by introducing AWS Elemental MediaPackage L2 constructs.
Constructs that will have a mixture of sensible defaults as well as methods to help build correct configurations
of Channel Groups, Channels and Origin Endpoints.

## Roles

| Role | User
|---------------------|------------------------------
| Proposed by | @jamiepmullan
| Author(s) | @jamiepmullan
| API Bar Raiser | @kumsmrit
| Stakeholders |
> See [RFC Process](https://github.com/aws/aws-cdk-rfcs#rfc-process) for details

## Workflow

- [x] Tracking issue created (label: `status/proposed`)
- [x] API bar raiser assigned (ping us at [#aws-cdk-rfcs](https://cdk-dev.slack.com/archives/C025ZFGMUCD) if needed)
- [x] Kick off meeting
- [x] RFC pull request submitted (label: `status/review`)
- [x] Community reach out (via Slack and/or Twitter)
- [x] API signed-off (label `status/api-approved` applied to pull request)
- [x] Final comments period (label: `status/final-comments-period`)
- [x] Approved and merged (label: `status/approved`)
- [x] Execution plan submitted (label: `status/planning`)
- [x] Plan approved and merged (label: `status/implementing`)
- [x] Implementation complete (label: `status/done`)

---

> Author is responsible to progress the RFC according to this checklist, and
apply the relevant labels to this issue so that the RFC table in README gets
updated.

Start by reviewing the approved RFC and execution-plan checklist referenced in this issue. The proposal covers Channel Groups, Channels, and Origin Endpoints for AWS Elemental MediaPackageV2, with sensible defaults and configuration helpers; completion is indicated by the checklist reaching “Implementation complete.”

Written by the indexing model from the issue text.