fix issue of plugin config reload dynamically failure

[lilai23]

What type of PR is this?

Bug

What this PR does / why we need it?

Add a custom yaml constructor for snakeyaml to make the same plugin config string can be loaded by new pluginclassloader rather than old pluginclassloader when install a plugin at the second time

Which issue(s) this PR fixes？

Fixes #1520

Does this PR introduce a user-facing change?

No

Checklist

• Make sure there is a GitHub_issue related with this PR before you start working on it.
• Make sure you have squashed your change to one single commit.
• GitHub Actions works fine in this PR.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 21 lines in your changes are missing coverage. Please review.

Flag	Coverage Δ	Complexity Δ
unittests	43.00% <0.00%> (-0.04%)	181.00 <0.00> (ø)

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

Files	Coverage Δ	Complexity Δ
...rmant/core/config/strategy/LoadConfigStrategy.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...rmant/implement/config/LoadPropertiesStrategy.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...ain/java/io/sermant/core/config/ConfigManager.java	6.89% <0.00%> (ø)	0.00 <0.00> (ø)
...ermant/core/plugin/config/PluginConfigManager.java	14.70% <0.00%> (-0.45%)	0.00 <0.00> (ø)
.../io/sermant/implement/config/LoadYamlStrategy.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...rmant/implement/config/SermantYamlConstructor.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)

... and 2 files with indirect coverage changes