[MI-100] Check connection status before loading the grid

[joseconsador]

Do not display Create Ticket and Dashboard/Grid if the extension is not setup properly.

related PR: #77

Steps to reproduce:

1. Login to the magento backend.
2. Go to Zendesk > Configuration.
3. In the General tab, make all fields empty except for Zendesk Domain.
   In the Admin Backend tab, set "Show support tickets on admin dashboard" to "Yes".
4. Click Save.
5. Go to Zendesk > Dashboard

Expected Result:

1. "Couldn't authenticate you" should appear as an error message.
2. On step Support for French, German, Japanese + more #5 - the configuration notice should be displayed

Actual Result:

1. A php warning (attached) appears, along with the standard error message.

1. On step Support for French, German, Japanese + more #5 - a fatal error is thrown and halts the process (attached)

/cc @miogalang @jwswj @mmolina @iandjx

References

• Jira link: https://zendesk.atlassian.net/browse/MI-100

QA notes

• Developer mode must be enabled

Risks

• Medium - Extension functionality may be affected.

[miogalang]

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[jwswj]

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