Enhancements to `generate` command

[bz888]

Prerequisites

Description

• Regenerate same abi for generate command Currrently, if you have a existing generated handler file, if you regenerate with the same abi, it will throw. we want to be able read existing handler file, and append missing abi events/functions.

• Generate according to given network Currently, this only works on ethereum manifests, we should add validators to the command and support more in the future.

• Generate from scratch ?

• Config startBlock via address If address is provided it should default startBlock to its contract creation

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?