fix RootConfig and getty-session-param

[quiet-xu]

What this PR does:
1.When init of rootConfig is used, var rootConfig is not configured. This variable is default by default, rootConfig parameter should be given after init，If this is not done, GetRootConfig() will not get the correct value.
2. The GettySessionParam serialization alias is missing, which causes the content to not be configured.
Which issue(s) this PR fixes:
Fixes #
Fixed thatGetRootConfig() could not get parameters correctly
Fixed that GettySessionParam could not be serialized correctly

• All ut passed (run 'go test ./...' in project root)
• After go-fmt ed , run 'go fmt project' using goland.
• Golangci-lint passed, run 'sudo golangci-lint run' in project root.
• After import formatted, (using imports-formatter to run 'imports-formatter .' in project root, to format your import blocks, mentioned in CONTRIBUTING.md above)
• Your new-created file needs to have apache license at the top, like other existed file does.
• All integration test passed. You can run integration test locally (with docker env). Clone our dubbo-go-samples project and replace the go.mod to your dubbo-go, and run 'sudo sh start_integration_test.sh' at root of samples project root. (M1 Slice is not Support)

[codecov-commenter]

Codecov Report

Merging #1802 (a55d078) into 3.0 (97f45f4) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              3.0    #1802      +/-   ##
==========================================
- Coverage   47.58%   47.56%   -0.02%     
==========================================
  Files         262      262              
  Lines       15114    15115       +1     
==========================================
- Hits         7192     7190       -2     
- Misses       7137     7139       +2     
- Partials      785      786       +1     

Impacted Files	Coverage Δ
remoting/getty/config.go	66.32% <ø> (ø)
config/root_config.go	69.79% <100.00%> (+0.15%)	⬆️
registry/nacos/listener.go	78.26% <0.00%> (-2.61%)	⬇️
cluster/loadbalance/p2c/loadbalance.go	76.36% <0.00%> (ø)

---

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 97f45f4...a55d078. Read the comment docs.