Restore Metadata

[josephjclark]

Description

This PR ports the legacy metadata service into the new collaborative editor

(no issue but it came out of #4386 )

Background

Metadata in this context refers to database/entity metadata pulled from the target backend service. So if you're editing a Salesforce step, the metadata is all the sObjects in the Salesforce instance the credential points to. If you're editing DHIS2, it's all the entities and attributes and stuff defined in the DHIS2 instance your credential points to.

Metadata was a bit of an experiment we did back in the day that never quite took off. We only support metadata for dhis2 and salesforce.

Metadata shows up in two places:

• The Metadata tab provides a nice list of all the metadata entities available. Users might want to refer to these things while writing job code
• In the code editor, we provide code assist based on metadata. We do this very very selectively and it's very very cool. See validation steps for more details.

Validation steps

1. Create a DHIS2 step
2. Create a credential with url https://play.im.dhis2.org/stable-2-42-3-1 user admin and password district
3. The Metadata tab should be populated with entities from the DHIS2 backend
4. Start typing create() (you should get code assist but maybe try ctrl + space)
5. You should get code assist for the first argument (a string ,try tracked-entity)
6. You should get code assist for the second argument. Start typing to the code below - you should get magic code assist on the attribute value)

create('tracked-entities', {
  attributes: [{
    attribute: 
  }]
})

AI Usage

Please disclose whether you've used AI anywhere in this PR (it's cool, we just
want to know!):

• I have used Claude Code
• I have used another model
• I have not used AI

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Responsible AI Policy

[josephjclark]

I'll need to rebase this on make-intellisense-great-again before review