Lower discount level threshold

[DylanVerstraete]

Currently these discount levels are implemented

    // https://wiki.threefold.io/#/threefold__grid_pricing
    let discount_received = match discount_level.floor().to_num::<u64>() {
        d if d >= 3 && d < 6 => types::DiscountLevel::Default,
        d if d >= 6 && d < 12 => types::DiscountLevel::Bronze,
        d if d >= 12 && d < 36 => types::DiscountLevel::Silver,
        d if d >= 36 => types::DiscountLevel::Gold,
        _ => types::DiscountLevel::None,
    };

All discount thresholds should be halfed

[renauter]

these manual link should be updated once in mainnet:

• https://library.threefold.me/info/manual/#/threefold__pricing?id=discount-levels
• https://library.threefold.me/info/manual/#/manual__proof_of_utilization_manual?id=discount-on-staked-tokens

[mohamedamer453]

Verified form #638
The discount levels were lowered to half as originally mentioned in the issue.

Manual still not updated with the new prices and should be updated in threefoldtecharchive/info_manual3#164 once it's released on mainnet.

Will also check the pricing calculator available in the dashboard to verify if it will need updates regarding this issue.