Subscription support for migrations

[bz888]

Prerequisites

• [x] Are you running the latest version(s)?
• [x] Have you searched the documentation for your issue?
• [x] Did you search for an existing issue or pull request?

Description

Currently the Schema Migration feature does not support subscription

Details

These details can help to reproduce the environment the issue is occurring

Local Environment: [You can get this information from executing subql version.] Query Version: [What is the version of the query service?] Indexer Version: [What is the version of the indexer service?] Network Details:

• [Network]
• [Block height, a block height where the issue is happening]
• [Dictionary endpoint, if used]

Steps to Reproduce

1. [First Step]
2. [Second Step]
3. [and so on...]

Example project: [A link to a minimal example that can reproduce the issue]

Expected behavior: [What you expected to happen]

Actual behavior: [What actually happened]

Any other information

Is there any other information you would like to add?