Increase minimum commission rate to 5%

Set the minimum commission rate to 5%. \n \n We have to build an healthier network : the competition to attract delegator is toxic and force others to lower their commission to attract people. We can agree on the fact that setting a minimum commission will justly reward contributors and avoid the validators spamming Juno Telegram channel and (0% fees). Validators also have more incentive to participate in the community and on the project (like Osmosis) rather than relying on their commission rate to attract delegations \n \n An idea will be to use the same code as Osmosis to make that. \n \n Find and contribute to the initial discussion here: https://github.com/CosmosContracts/juno/issues/17