UI: Please change memory setting in flex compute offering from MiB to GiB

### The required feature described as a wish

As a user, I'd like to be able to set the memory size of my instances in GiB without having to calculate the correct MiB value.
Entering values in MiB tends to lead to entering round numbers of 1,000. This then results in odd GiB values.
If a VM with less than 1 GiB is ever actually needed, you can enter 0.5 GiB, for example.
However, this use case is likely to occur much less frequently than higher GiB values.

Maybe it could include a drop-down menu next to the value that uses GiB as the default but also allows MiB to be selected. But I think GiB is the most helpful for most people.

先找出 flex compute 方案的 UI，以及目前接受 MiB 數值的記憶體欄位，接著檢查附近的 UI 測試。完成的標準是使用者預設可以以 GiB 輸入記憶體，包括 0.5 這類分數值；如果現有設計支援單位選擇器，還應提供所要求的 MiB 選項。

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