refactor: change go module to dashpay/tenderdash

[shotonoff]

Issue being fixed or feature implemented

To verify light-blocks from an external blockchain via IBC, Tenderdash must use the original light-client.
The easiest way is to add Tendermint as dependency to the project, but to be able to do it we need to change the module in go.mod

What was done?

• Changed project module to github.com/dashpay/tenderdash in go.mod
• Updated imports in *.go to support a new module name
• Added github.com/tendermint/tendermint v0.34.21

How Has This Been Tested?

Unit/ E2E Tests

Breaking Changes

N/A

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone