feat(application): more precise plan upgrade/downgrade direction

[LorrisSaintGenez]

What

• application upgrade/downgrade now list only the plans relevant to the current plan, in the order returned by the plans endpoint (no hardcoding): upgrade shows higher tiers, downgrade shows lower tiers.
• Read the current plan from the application data (attributes.plan.label) and match it to the self-serve list by label.
• No-op with a message when already at the highest/lowest plan, or when the requested plan equals the current one.
• Explicit --plan still overrides direction; unknown/legacy plans fall back to the full list.

Test

go run ./cmd/algolia application upgrade --dry-run     # higher tiers only / "nothing to upgrade to"
go run ./cmd/algolia application downgrade --dry-run   # lower tiers only
go run ./cmd/algolia application upgrade --plan <current-plan>  # "already on … no change needed"

GROUT-361

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 32 complexity · 8 duplication

Metric	Results
Complexity	32
Duplication	8

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_{TIP This summary will be updated as you push new changes.}