Adding metadata and expires_at to Secure Files

What does this MR do and why?

As the first MR to be extracted from this POC !97548 (closed), this MR adds two fields to the ci_secure_files table in the database. One field is a jsonb metadata field, and the other is the expires_at timestamp. These fields will be used to store metadata for file types we are able to parse. For more context, please see this issue #374949 (closed), and the original POC MR.

Migration Output

rake db:migrate:ci
ci: == 20220921174815 AddSecureFilesMetadata: migrating ===========================
ci: -- add_column(:ci_secure_files, :metadata, :jsonb)
ci:    -> 0.0038s
ci: -- add_column(:ci_secure_files, :expires_at, :datetime_with_timezone)
ci:    -> 0.0005s
ci: == 20220921174815 AddSecureFilesMetadata: migrated (0.0048s) ==================

Rollback Output

rake db:rollback:ci
ci: == 20220921174815 AddSecureFilesMetadata: reverting ===========================
ci: -- remove_column(:ci_secure_files, :expires_at, :datetime_with_timezone)
ci:    -> 0.0028s
ci: -- remove_column(:ci_secure_files, :metadata, :jsonb)
ci:    -> 0.0004s
ci: == 20220921174815 AddSecureFilesMetadata: reverted (0.0052s) ==================

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