Add polkastats identity

[mariopino]

Closes #117

Description:

Add polkastats_identity table and insert current data taken from old V2 backend.

Thank you! 🚀

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For contributor:

• [ ] Reviewed Files changed in the github PR explorer
• [ ] Attach screenshots of the UI components on the PR description (if applicable)
• [ ] Scope of work approved for big PRs

For reviewer:

• [ ] Manually tested the changes on the UI