Update ACS Email python SDK for inline attachments

[natekimball-msft]

Description

This update introduces the new EmailAttachment property contentId, the presence of which will be used to mark an attachment for inline rendering. The contentId property should be referenced in the HTML body of the email attachment.

Link to swagger spec API: Azure/azure-rest-api-specs#29699

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[DominikMe]

Lgtm with comments