chore: catch error when demo server start

[Frapschen]

It's better to catch any error during the demo OpAMP Server starting. e.g. the 4320 port already in use.

before this PR: if we start an OpAMP Server in the background, and then start another OpAMP Server, we will get:

fraps@CMQ server % ./bin/server 
2024/01/10 10:46:33.961345 [MAIN] OpAMP Server starting...
2024/01/10 10:46:33.963579 [MAIN] OpAMP Server running...

however, it fails to start the OpAMP Server.

with this PR's enhance:

fraps@CMQ server % ./bin/server
2024/01/10 10:49:12.296051 [MAIN] OpAMP Server starting...
2024/01/10 10:49:12.298014 [OPAMP] OpAMP server start fail: listen tcp 127.0.0.1:4320: bind: address already in use

It response the real status of the OpAMP server.

[codecov]

Codecov Report

Attention: 130 lines in your changes are missing coverage. Please review.

Comparison is base (efddaa2) 76.11% compared to head (51e1974) 72.65%.
Report is 42 commits behind head on main.

Files	Patch %	Lines
internal/certs.go	0.00%	118 Missing ⚠️
client/internal/httpsender.go	88.00%	2 Missing and 1 partial ⚠️
client/internal/mockserver.go	85.71%	2 Missing and 1 partial ⚠️
server/httpconnection.go	0.00%	2 Missing ⚠️
client/internal/clientcommon.go	90.90%	1 Missing ⚠️
client/internal/packagessyncer.go	0.00%	1 Missing ⚠️
client/internal/receivedprocessor.go	90.90%	1 Missing ⚠️
server/serverimpl.go	95.65%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #236      +/-   ##
==========================================
- Coverage   76.11%   72.65%   -3.47%     
==========================================
  Files          24       25       +1     
  Lines        1834     2022     +188     
==========================================
+ Hits         1396     1469      +73     
- Misses        326      443     +117     
+ Partials      112      110       -2     

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[srikanthccv]

Thank you

[tigrannajaryan]

Thank you @Frapschen