Webex v0.2: Cancel button on upcoming meetings list

Description

From https://help.webex.com/en-us/n6dr138/Cisco-Webex-Meetings-for-Slack#id_112263:

Put a cancel button in the custom post for a scheduled meeting.

QA Test Steps

None

Status

Mana

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Assignee

Unassigned

QA Assignee

None

Reporter

Christopher Poile

Epic Link

Fix versions

Mattermost Team

Integrations

Sprint

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Labels

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QA Testing Areas

None

GitHub Issue

None

Components

None
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