[Improve] Use metric_dict to replace hardcode arg in evaluate

[dreamerlin]

def evaluate(self,
             ...
             topk=(1, 5),
             ...):

to

def evaluate(self,
             ...
             metric_dict=dict(topk=(1, 5)),
             ...):

to avoid hardcoded argument for evaluate

[codecov]

Codecov Report

Merging #286 into master will decrease coverage by 0.17%.
The diff coverage is 63.75%.

@@            Coverage Diff             @@
##           master     #286      +/-   ##
==========================================
- Coverage   82.56%   82.39%   -0.18%     
==========================================
  Files          95       95              
  Lines        6867     6777      -90     
  Branches     1126     1099      -27     
==========================================
- Hits         5670     5584      -86     
- Misses        984      986       +2     
+ Partials      213      207       -6     

Flag	Coverage Δ
unittests	82.39% <63.75%> (-0.18%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmaction/datasets/audio_dataset.py	73.68% <ø> (-10.10%)	⬇️
mmaction/datasets/audio_feature_dataset.py	73.68% <ø> (-10.10%)	⬇️
mmaction/datasets/image_dataset.py	83.33% <ø> (ø)
mmaction/datasets/rawframe_dataset.py	86.56% <ø> (+8.23%)	⬆️
mmaction/datasets/video_dataset.py	66.66% <ø> (-15.88%)	⬇️
mmaction/datasets/activitynet_dataset.py	92.59% <50.00%> (-2.46%)	⬇️
mmaction/datasets/ssn_dataset.py	92.66% <50.00%> (-0.80%)	⬇️
mmaction/datasets/base.py	60.00% <66.10%> (+4.04%)	⬆️
mmaction/datasets/hvu_dataset.py	67.10% <66.66%> (-0.47%)	⬇️
mmaction/datasets/ava_dataset.py	89.62% <100.00%> (ø)
... and 3 more

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[dreamerlin]

@innerlee @SuX97 Ready now

[innerlee]

hope this one does not cause trouble for users