[GRIN-Wallet] change accept_fee_base for - testnet only

[MCM-Mike]

Description:
This test is for testnet only.

Prerequisites:
Grin-Node fully synced and two (2) Grin-Wallets ready to use.
Add the following line to your grin-wallet.toml file on both wallets. Test each cases individually.

Case 1)

#Minimum acceptable fee per unit of transaction weight
accept_fee_base = 499_999

Case 2)

#Minimum acceptable fee per unit of transaction weight
accept_fee_base = 500_000

and send GRINs from one wallet to the other wallet.
Make sure on both wallets have been applied the changes.

Expected result:
For case 1) the transaction should not confirm.
For case 2) the transaction will confirm normally.

Include the output of command

grin-wallet -V

and your environment

uname -a

[marekyggdrasil]

My grin-node 5.0.0-rc.1 properly synced and is running on testnet. I also initiated a test wallet with grin-wallet 5.0.0-rc.1 however I am unable to reach the local node due to mimblewimble/grin-wallet#561

Looking for an alternate solution.