Adds composer.json to composer metadata in db

What does this MR do?

Change composer package creating service to save the composer.json file to DB.

This will be needed for quicker retrieval of the file in the upcoming !32390 (merged) MR.

Rollback output

== 20200615083635 AddComposerJsonToMetadata: reverting ========================
-- remove_column(:packages_composer_metadata, :composer_json, :jsonb, {:default=>{}, :null=>false})
   -> 0.0075s
== 20200615083635 AddComposerJsonToMetadata: reverted (0.0099s) ===============

Migrate output

== 20200615083635 AddComposerJsonToMetadata: migrating ========================
-- add_column(:packages_composer_metadata, :composer_json, :jsonb, {:default=>{}, :null=>false})
   -> 0.0077s
== 20200615083635 AddComposerJsonToMetadata: migrated (0.0077s) ===============

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #214731 (closed)