Add a priority for sponsor tier ordering

[AetherUnbound]

Previously, sponsor tiers were inserted when the app was created and that ordering of database object IDs was used to determine (sometimes contextually incorrect) order.

This PR adds a new field on the SponsorTier snippet which allows us to define a "priority". The tiers (within the category) are then ordered by the inverse of this priority on the page. Meaning, tiers with higher priority are shown higher in the page. I've tested this locally and asserted that a "super diamond" tier with a higher priority than 0 shows up above Diamond, even though the latter was added first.

Because the priority is also an arbitrary number, we can just choose increments of 10 in case we add any other tiers in between!