doc: use 3 issue template for better community experience

[imbajin]

At present, there are 3 issue template and 1 config file:

• Bug Report
• Feature Request
• Ask question (Guide)

And simplify the issue template to improve the user's willingness to fill in, like this:

BUG like:

Question like:

[codecov]

Codecov Report

Merging #1453 (fdd006c) into master (1ede97c) will increase coverage by 0.42%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1453      +/-   ##
============================================
+ Coverage     61.80%   62.23%   +0.42%     
- Complexity     5840     5860      +20     
============================================
  Files           381      381              
  Lines         32148    32148              
  Branches       4504     4504              
============================================
+ Hits          19869    20007     +138     
+ Misses        10231    10085     -146     
- Partials       2048     2056       +8     

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/com/baidu/hugegraph/task/HugeTask.java	69.53% <0.00%> (-0.31%)	81.00% <0.00%> (-1.00%)
.../baidu/hugegraph/backend/query/ConditionQuery.java	86.40% <0.00%> (+0.40%)	106.00% <0.00%> (+1.00%)
.../backend/store/cassandra/CassandraSessionPool.java	57.14% <0.00%> (+1.02%)	11.00% <0.00%> (ø%)
...egraph/backend/store/cassandra/CassandraShard.java	52.77% <0.00%> (+1.85%)	11.00% <0.00%> (ø%)
...h/backend/store/scylladb/ScyllaDBTablesWithMV.java	96.03% <0.00%> (+96.03%)	10.00% <0.00%> (+10.00%)
...graph/backend/store/scylladb/ScyllaDBFeatures.java	100.00% <0.00%> (+100.00%)	3.00% <0.00%> (+3.00%)
.../backend/store/scylladb/ScyllaDBStoreProvider.java	100.00% <0.00%> (+100.00%)	7.00% <0.00%> (+7.00%)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1ede97c...fdd006c. Read the comment docs.