Increase Max Commission Rate

[cmwaters]

V4 introduced an upper bound on the maximum commission rate (25%). As well as documenting it (as described here), we want to consider increasing the limit (I would suggest to 35%) for v7 to give room for validators to increase it if they want.

To do:

• Decide if we also want to raise the minimum commission rate as well (for v7) cc @liamsi
• Write a short CIP for the parameter changes
• Update one or both parameters in the SDK. Make sure the change comes into effect upon the v7 upgrade height (i.e. migration is necessary if the minimum changes)