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

[andrewazores]

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---

Fixes: #1698

Description of the change:

Modifies the DiscoveryStorage plugin ping logic to be tolerant of request failures or network exceptions by remapping the ping task future to one that logs exceptions but does not propagate the Future failure to the aggregate Future representing the entire task.

Motivation for the change:

When this plugin ping prune task is done periodically failures are already ignored. However, when this task is done initially at startup to check plugin registrations already present in the database from the last run, ping failures would fail the whole task, cascading into failing the server startup. This should not happen - the server is not dependent upon the discovery plugins and can handle their absence fine, so it should not be startup-blocking if an exception occurs when probing them.

How to manually test:

1. Tough to nail down because it requires a narrow condition where the discovery plugin is present but a network error occurs during the registration ping request, ex. the network stack says that the plugin hostname can be resolved but the connection is refused because the plugin JVM is not yet ready to accept connections.

[github-actions]

Hi @andrewazores! Add at least one of the required labels to this PR

Required labels are : chore,ci,cleanup,docs,feat,fix,perf,refactor,style,test

[github-actions]

Hi @andrewazores! Add at least one of the required labels to this PR

Required labels are : chore,ci,cleanup,docs,feat,fix,perf,refactor,style,test

[github-actions]

Hi @andrewazores! Add at least one of the required labels to this PR

Required labels are : chore,ci,cleanup,docs,feat,fix,perf,refactor,style,test

[andrewazores]

/build_test

[andrewazores]

https://github.com/cryostatio/cryostat/actions/runs/6470118720

[github-actions]

ARCH	IMAGE
amd64	ghcr.io/cryostatio/cryostat:pr-1700-1c1d3b17c939d749b8192078af7ef97eb87573ec-linux-amd64
arm64	ghcr.io/cryostatio/cryostat:pr-1700-1c1d3b17c939d749b8192078af7ef97eb87573ec-linux-arm64

To run smoketest:

# amd64          
CRYOSTAT_IMAGE=ghcr.io/cryostatio/cryostat:pr-1700-1c1d3b17c939d749b8192078af7ef97eb87573ec-linux-amd64 sh smoketest.sh

# or arm64
CRYOSTAT_IMAGE=ghcr.io/cryostatio/cryostat:pr-1700-1c1d3b17c939d749b8192078af7ef97eb87573ec-linux-arm64 sh smoketest.sh

[aali309]

Looks good to me