fix(discovery): do not fail startup if plugin ping fails (backport #1700)

[mergify]

This is an automatic backport of pull request #1700 done by Mergify.

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[andrewazores]

/build_test

[andrewazores]

https://github.com/cryostatio/cryostat/actions/runs/6474928206

[github-actions]

ARCH	IMAGE
amd64	ghcr.io/cryostatio/cryostat:pr-1701-cc59eeccfc1725d38135c116369746bc443070bb-linux-amd64
arm64	ghcr.io/cryostatio/cryostat:pr-1701-cc59eeccfc1725d38135c116369746bc443070bb-linux-arm64

To run smoketest:

# amd64          
CRYOSTAT_IMAGE=ghcr.io/cryostatio/cryostat:pr-1701-cc59eeccfc1725d38135c116369746bc443070bb-linux-amd64 sh smoketest.sh

# or arm64
CRYOSTAT_IMAGE=ghcr.io/cryostatio/cryostat:pr-1701-cc59eeccfc1725d38135c116369746bc443070bb-linux-arm64 sh smoketest.sh