fix: hide IntegrationPackage.ID from JSON

[mdelapenya]

What does this PR do?

It uses JSON tags to hide the field from JSON marshall/unmarshall operations.

Why is it important?

This way, the requests to Kibana won't contain that field, honouring Kibana's contract about fleet schema.

We are receiving a payload when getting integrations from Kibana, and that payload contains the ID, that's why we added the field to the struct. When sending POST requests to kibana to add an integration package to a policy, this struct is converted to JSON and sent as payload. But Kibana spec does not allow the ID field in its schema, and after elastic/kibana#99886 Kibana is stricter than before, as it fails with a HTTP 400 error code:

Error: could not add package to policy; API status code = 400; response body = {"statusCode":400,"error":"Bad Request","message":"[request body.package.id]: definition for this key is missing"}

In the past, before that Kibana PR, it simply ignored the field, which makes me think about a third party dependency in Kibana adding the new strictness.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

Author's Checklist

• @kpollich I'm sending this workaround here too trying to simplify the fix in Kibana

How to test this PR locally

$ TAGS="linux_integration" TIMEOUT_FACTOR=3 LOG_LEVEL=TRACE BEATS_USE_CI_SNAPSHOT=false DEVELOPER_MODE=true make -C e2e/_suites/fleet functional-test

Related issues

• Relates [Fleet] Include ID field in packages on get/create kibana#100908
• Relates [7.x] [Dashboard/Reporting] Fix print layout report (#99458) kibana#99886
• Relates [Fleet] Allow Package ID in Create Package Policy requests kibana#100897

[elasticmachine]

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• Build Cause: Pull request #1211 updated

• Start Time: 2021-06-01T04:59:15.079+0000

• Duration: 21 min 5 sec

• Commit: aa7b3d4

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Test	Results
Failed	0
Passed	160
Skipped	0
Total	160

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Test stats 🧪

Test	Results
Failed	0
Passed	160
Skipped	0
Total	160