feat:refactor SDKContext as static.

[SkyeBeFreeman]

PR Type

Refactoring (no functional changes, no api changes).

Describe what this PR does for and how you did.

Adding the issue link (#xxx) if possible.

fixes #982
fixes #984

Note

Checklist

• Add information of this PR to CHANGELOG.md in root of project.
• Add documentation in javadoc or comment below the PR if necessary.

Checklist (Optional)

• Will pull request to branch of 2020.0.
• Will pull request to branch of 2022.0.

[codecov]

Codecov Report

Merging #1001 (c377b60) into 2021.0 (a73f0e1) will increase coverage by 0.09%.
The diff coverage is 92.30%.

@@             Coverage Diff              @@
##             2021.0    #1001      +/-   ##
============================================
+ Coverage     82.93%   83.02%   +0.09%     
- Complexity     1586     1608      +22     
============================================
  Files           238      239       +1     
  Lines          5245     5321      +76     
  Branches        611      621      +10     
============================================
+ Hits           4350     4418      +68     
- Misses          540      549       +9     
+ Partials        355      354       -1     

Impacted Files	Coverage Δ
...laris/context/config/PolarisContextProperties.java	95.12% <66.66%> (+0.38%)	⬆️
...cloud/polaris/registry/PolarisServiceRegistry.java	71.42% <76.47%> (-0.14%)	⬇️
...loud/polaris/context/PolarisSDKContextManager.java	92.95% <92.95%> (ø)
...config/PolarisCircuitBreakerAutoConfiguration.java	100.00% <100.00%> (ø)
...eactivePolarisCircuitBreakerAutoConfiguration.java	100.00% <100.00%> (ø)
...onfig/PolarisConfigBootstrapAutoConfiguration.java	85.71% <100.00%> (ø)
.../polaris/DiscoveryPropertiesAutoConfiguration.java	100.00% <100.00%> (ø)
...oud/polaris/discovery/PolarisDiscoveryHandler.java	100.00% <100.00%> (+17.39%)	⬆️
...h/PolarisRefreshApplicationReadyEventListener.java	76.19% <100.00%> (ø)
...discovery/refresh/PolarisRefreshConfiguration.java	100.00% <100.00%> (ø)
... and 7 more

... and 3 files with indirect coverage changes

[ShanyouYu-Sean]

LGTM