Ordering policy of resource presets

[achimnol]

Currently, resource presets are only alphabetically ordered (when requesting a specific set of resource presets by names):

backend.ai/src/ai/backend/manager/models/resource_preset.py

Line 88 in dec5284

.order_by(resource_presets.c.name)

or unordered (when listing all resource presets at once):

backend.ai/src/ai/backend/manager/models/resource_preset.py

Line 70 in dec5284

query = sa.select([resource_presets]).select_from(resource_presets)

Let's add an option to explicitly order them:

• LEXICOGRAPHIC_ASC: alphabetically ordered
• LEXICOGRAPHIC_DESC: alphabetically reverse-ordered (new)
• RESOURCE_SIZE_ASC: smaller resource preset first (new)
• RESOURCE_SIZE_DESC: larger resource preset first (new)

To define the relative size of resource presets, we should have a resource slot precedence to make them comparable with each other. Fortunately, we already apply a similar precedence-based ordering when calculating the optimal hardware layouts in the agents as the allocation order config:

backend.ai/configs/agent/sample.toml

Line 286 in dec5284

allocation-order = ["cuda", "rocm", "tpu", "cpu", "mem"]

We also need to add a new, similar shared config option to separately set the resource slot precedence for the UI displays.