Add info column into security_scans table

What does this MR do?

This MR introduces a new column for the security_scans table called info. The column will store the error & debug information to inform the users about the issues that happened during the report ingestion process. We've decided to use a JSONB column to store this information as the schema can change in the near future. We are also not introducing any index for this column as it will only be read-only.

Database Review

rake db:migrate

== 20210308125742 AddInfoColumnIntoSecurityScansTable: migrating ==============
-- add_column(:security_scans, :info, :jsonb, {:null=>false, :default=>{}})
   -> 0.0032s
== 20210308125742 AddInfoColumnIntoSecurityScansTable: migrated (0.0033s) =====

rake db:rollback

== 20210308125742 AddInfoColumnIntoSecurityScansTable: reverting ==============
-- remove_column(:security_scans, :info, :jsonb, {:null=>false, :default=>{}})
   -> 0.0028s
== 20210308125742 AddInfoColumnIntoSecurityScansTable: reverted (0.0046s) =====

Related to #321917 (closed).

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
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• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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Security

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• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
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