v11.0 Notice

[amyblais]

Summary

• In-product notice for v11.0 release.

Screenshots of the modals or screens in all target clients (required)

• The server upgrade image should display https://github.com/mattermost/notices/blob/master/images/server_upgrade.png along with the text from https://github.com/mattermost/notices/pull/452/files#diff-11766faeb8c25f77d7dbf8e61fd0e9fc8cd1a08858d6b1f8867715a570bfd9d9R82.

Test environment (required)

• Server versions - v11.0 and v10.12

Test steps and expectation (required)

• Spin up a v10.12 server - the notice should appear.
• Spin up a v11.0 server - the notice should not appear.

[yasserfaraazkhan]