feat: add support for gravity chain in EVM plugin

[Stumble]

Relates to

No specific issue related.

Risks

Low. This PR only adds gravity to templates and types.

Background

What does this PR do?

• Updated fromChain and toChain types in templates/index.ts to include "gravity".
• Added "gravity" to the EvmPluginConfig interface in types/index.ts.

This enhancement allows the EVM plugin to handle transactions involving the "gravity" chain.

What kind of change is this?

Features (non-breaking change which adds functionality)

Documentation changes needed?

My changes do not require a change to the project documentation.

Testing

Where should a reviewer start?

Detailed testing steps

[JoeyKhd]

lgtm