Fix args cannot take effect when dynamic install sermant agent with external agent and instance selectable condition in Backend

[lilai23]

What type of PR is this?

Bug

What this PR does / why we need it?
fix issues:
(1) Args cannot take effect when dynamic install sermant agent with external agent
(2) Offline instance can be selected in Sermant Backend

Which issue(s) this PR fixes？

Fixes #1705

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 25.00000% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...c/main/java/io/sermant/core/AgentCoreEntrance.java	0.00%	7 Missing ⚠️
...ore/service/metric/entity/MetricCommonTagEnum.java	0.00%	1 Missing ⚠️
...mant/flowcontrol/DispatcherServletInterceptor.java	0.00%	1 Missing ⚠️

Flag	Coverage Δ	Complexity Δ
unittests	43.82% <25.00%> (-0.01%)	181.00 <0.00> (ø)

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

Files with missing lines	Coverage Δ	Complexity Δ
...java/io/sermant/core/ext/ExternalAgentManager.java	46.93% <100.00%> (ø)	0.00 <0.00> (ø)
.../java/io/sermant/core/service/metric/api/Tags.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...mant/implement/service/xds/handler/XdsHandler.java	48.14% <ø> (+0.58%)	0.00 <0.00> (ø)
...ment/service/xds/utils/RdsProtocolTransformer.java	40.19% <ø> (ø)	0.00 <0.00> (ø)
...ry/condition/ResetBeforeRequestErrorCondition.java	50.00% <100.00%> (ø)	0.00 <0.00> (ø)
...ore/service/metric/entity/MetricCommonTagEnum.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...mant/flowcontrol/DispatcherServletInterceptor.java	50.00% <0.00%> (ø)	0.00 <0.00> (ø)
...c/main/java/io/sermant/core/AgentCoreEntrance.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)

... and 2 files with indirect coverage changes