feat: add Agent to Filecoin.Version !

[LesnyRumcajs]

Related Issues

Closes #12904

Proposed Changes

Added Agent to the Filecoin.Version. Depending on the client's deserialization capabilities, this is a potentially breaking change.

Additional Info

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• PR title conforms with contribution conventions
• Update CHANGELOG.md or signal that this change does not need it per contribution conventions
• New features have usage guidelines and / or documentation updates in
  • Lotus Documentation
  • Discussion Tutorials
• Tests exist for new functionality or change in behavior
• CI is green

[github-actions]

Please update the PR title to match https://github.com/filecoin-project/lotus/blob/master/CONTRIBUTING.md#pr-title-conventions

PR title now matches the required format.

[rjan90]

Tested in a devnet:

curl -X POST http://localhost:1234/rpc/v0 \
     -H "Content-Type: application/json" \
     -d '{
           "jsonrpc": "2.0",
           "method": "Filecoin.Version",
           "params": [],
           "id": 1
         }'
{"id":1,"jsonrpc":"2.0","result":{"Version":"1.32.1-dev+2k+git.8d6d554e8","APIVersion":66816,"BlockDelay":4,"Agent":"lotus"}}

[rjan90]

Looks good to me based on the testing I have done, but would be good to have an additional ✅ from maybe @masih ?