Load env for `gitlab:db:create_dynamic_partitions`

What does this MR do?

Set :environment as an explicit dependency for gitlab:db:create_dynamic_partitions so you can run it as a standalone task.

Currently you get the below error. This works fine most of the time because it's called from db:migrate which already loads the environment, but if you want to run the partition creation manually, you can't.

rails gitlab:db:create_dynamic_partitions
rails aborted!
NameError: uninitialized constant Gitlab::Database
Did you mean?  DatabaseCleaner
/Users/pbair/Projects/gitlab-development-kit/gitlab/lib/tasks/gitlab/db.rake:118:in `block (3 levels) in <main>'

Caused by:
NameError: uninitialized constant Gitlab::Database
Did you mean?  DatabaseCleaner
/Users/pbair/Projects/gitlab-development-kit/gitlab/lib/tasks/gitlab/db.rake:118:in `block (3 levels) in <main>'
Tasks: TOP => gitlab:db:create_dynamic_partitions
(See full trace by running task with --trace)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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• I have self-reviewed this MR per code review guidelines.
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• This change is backwards compatible across updates, or this does not apply.

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Security

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