added method to delete member in conversations client

[SecondeJK]

This PR adds the delete method for a member in a conversation.

Description

Call $client->conversation()->deleteMember(CONVERSATION_ID, MEMBER_ID); to use

Motivation and Context

Missing methods

How Has This Been Tested?

Test added to cover completion.

Example Output or Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.