issue790 add context plugin

[SaberSola]

Fixes #790
Make sure that:

• You have read the contribution guidelines.
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed mvn clean install -Dmaven.javadoc.skip=true.

[codecov-io]

Codecov Report

Merging #894 (80dbca5) into master (e1e7779) will increase coverage by 0.04%.
The diff coverage is 82.75%.

@@             Coverage Diff              @@
##             master     #894      +/-   ##
============================================
+ Coverage     72.25%   72.29%   +0.04%     
- Complexity     1745     1755      +10     
============================================
  Files           303      304       +1     
  Lines          6877     6906      +29     
  Branches        782      786       +4     
============================================
+ Hits           4969     4993      +24     
- Misses         1508     1510       +2     
- Partials        400      403       +3     

Impacted Files	Coverage Δ	Complexity Δ
...l/plugin/contextpath/ContextPathMappingPlugin.java	82.14% <82.14%> (ø)	10.00 <10.00> (?)
...java/org/dromara/soul/common/enums/PluginEnum.java	100.00% <100.00%> (ø)	3.00 <0.00> (ø)

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