Update: Column Management Modal

[kaylachumley]

GH issue: https://issues.redhat.com/browse/RHCLOUD-34205

• Within modal: update action list gap spacing to use global/spacer/gap/action-to-action: 16px/spacer-300

• Within modal: font weight on heading needs to be updated to be bold to match the v6 modal styling: font-weight: var(--pf-v6-c-modal-box__title--FontWeight);

[kaylachumley]

global/spacer/gap/action-to-action => --pf-t--global--spacer--md