Fixed https://github.com/wso2/product-iots/issues/1671

[charithag]

Purpose

As a result of FCM API key is getting cached, once we change the FCM API key while running the server, it is required to restart the server. This fix avoids the server restarting when we change the FCM API key. Fixed https://github.com/wso2/product-iots/issues/1671

Goals

Get PushNotificationProvider dynamically based on the platform configurations

Approach

Update operation manager to get current platform configurations from registry on demand with a internal cache.

User stories

N/A, Bug fix

Release note

Fixed https://github.com/wso2/product-iots/issues/1671

Documentation

Link(s) to product documentation that addresses the changes of this PR. If no doc impact, enter “N/A” plus brief explanation of why there’s no doc impact

Training

N/A, Bug fix

Certification

N/A, Bug fix

Marketing

N/A, Bug fix

Automation tests

• Unit tests

  Code coverage 85%

• Integration tests

  Covered with existing tests

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

N/A, Bug fix

Related PRs

https://github.com/wso2/carbon-device-mgt-plugins/pull/887

Migrations (if applicable)

N/A, Bug fix

Test environment

Fedora 23 Linux 4.8.13-100.fc23.x86_64, Oracle JDK 1.8.0_91-b14, H2

Learning

N/A, Bug fix