add topics as yaml form instead of labels

.gitea/issue_template/proposal.yaml

@@ -14,13 +14,102 @@ body:
       placeholder: stofl, inspired by https://codeforces.com/problemset/problem/1/A
     validations:
       required: true
-  - type: markdown
+  - type: dropdown
+    id: round
     attributes:
-      value: |
-        ### Topics
-        
-        Relevant topics for this task.
-        Choose the corresponding *topic* labels for this issue on the right.
+      label: "Topics"
+      description: "Relevant topics for this task."
+      multiple: true
+      options:
+        - 2d segment tree
+        - 2sat
+        - 3d prefix sum
+        - adhoc
+        - aho-corasic
+        - amortization
+        - articulation points
+        - bellman-ford
+        - bfs
+        - bignum
+        - binary search
+        - binary search tree
+        - bipartite matching
+        - bridges
+        - brute force
+        - cartesian tree
+        - centroid decomposition
+        - combinatorics
+        - connected components
+        - convex hull
+        - convex hull trick
+        - deque
+        - dfs
+        - dijkstra
+        - divide and conquer
+        - dp
+        - edit distance
+        - fastpow
+        - fenwick tree
+        - floyd-warshall
+        - gcd
+        - geometry
+        - grahams scan
+        - graph
+        - greedy
+        - hashmap
+        - heap
+        - implementation
+        - interactive
+        - interval tree
+        - kmp
+        - kruskal
+        - lca
+        - lcd
+        - lcs
+        - line intersection
+        - lis
+        - map
+        - math
+        - matrix
+        - maxflow
+        - mcm
+        - median
+        - mer
+        - min-cost flow
+        - mst
+        - multimap
+        - multiset
+        - next permutation
+        - number theory
+        - offline processing
+        - output only
+        - path
+        - longest path in dag
+        - permutations
+        - precomputation
+        - prefix sum
+        - prim
+        - priority queue
+        - quad tree
+        - queue
+        - range minimum query
+        - scanline
+        - scc
+        - search
+        - segment tree
+        - set
+        - shortest path
+        - sorting
+        - stack
+        - string
+        - subsets
+        - toposort
+        - tree
+        - trivial
+        - union find
+        - warmup
+    validations:
+      required: false
   - type: markdown
     attributes:
       value: |