Adding notification for the user on a Websocket handshake failure

[rasika]

Purpose

On the device's realtime analytics page; unless specified and exempted websocket URL endpoint for the IoT Analytics Server will be failed without notifying the user. This PR resolves https://github.com/wso2/product-iots/issues/1659.

Goals

Adding notification for the user on a Websocket handshake failure

Approach

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User stories

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Release note

Adding notification for the user on a Websocket handshake failure

Documentation

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Training

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Certification

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Marketing

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Automation tests

• Unit tests

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• Integration tests

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Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines? yes
• Ran FindSecurityBugs plugin and verified report? yes
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets? yes

Samples

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Related PRs

https://github.com/wso2/carbon-device-mgt/pull/1177, https://github.com/wso2/product-iots/pull/1660

Migrations (if applicable)

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Test environment

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Learning

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