[NEW] Announcement component

[samad-yar-khan]

• [x] I have read the Contributing Guide - https://github.com/RocketChat/Rocket.Chat/blob/develop/.github/CONTRIBUTING.md#contributing-to-rocketchat doc
• [x] I have signed the CLA - https://cla-assistant.io/RocketChat/Rocket.Chat
• [x] Lint and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works (if applicable)
• [x] I have added necessary documentation (if applicable)
• [x] Any dependent changes have been merged and published in downstream modules

Issues

Mentioned in the issue #113

Proposed changes (including videos or screenshots)

• Add New Announcement Component which can display relevant announcement on any page using a helper function - getAnnouncementData('announcement_code').
• The component has been added to the layout and is only displayed when a relevant/published announcement is fetched using getAnnouncementData('announcement_code') code function and passed in the page props.
• Added announcement collection type / schema to store announcements in the database.
• Announcements have a publish_date and unpublish_date
  • Announcements are only displayed after the publish_date and before the unpublish_date
• Added a deleteOldAnnouncemts() helper function as a cron job which will run once a day and will delete any announcements which are supposed to be unpublished depending on the date. This will ensure that unwanted announcements do not clutter the database.
• At the time of data-initialization , the announcements in cms/config/initialData/announcemnets.json will populate the data base.

https://user-images.githubusercontent.com/70485812/160889912-0181fd56-e62d-416c-9c6d-0a92280bbc94.mp4

• Added Documentation for the usage of the component.

[samad-yar-khan]

@debdutdeb I have rebased the branch with the master branch and there are no more build errors. Build is not failing anymore 😅