fix(plugins/container): use an unique ctx for fetcher.

[FedeDP]

What type of PR is this?

/kind bug

Any specific area of the project related to this PR?

/area plugins

What this PR does / why we need it:

Podman relies upon context to store its connection infos. Using same ctx already used by the real Podman engine means that we are going to tamper with its connection info stored in the main ctx.

Instead, fetcher should use its own context.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[FedeDP]

This was causing:

panic: runtime error: index out of range [32] with length 32

goroutine 76 [running]:
net/url.escape({"container.id":"08491c4650e1","container.image.repository":"","container.image.tag":"","container.name":"","evt.args":"res=3 exe=/http-echo args=-text=hello. tid=20832(http-echo) pid=20832(http-echo) ptid=20830(conmon) cwd=<NA> fdlimit=1048576 pgft_maj=0 pgft_min=148 vm_size=705624 vm_rss=3740 vm_swap=0 comm=http-echo cgroups=cpuset=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.cpu=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.cpuacct=/.io=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.memory=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.devices=/.freezer=/.net_cls=/.perf_event=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.net_prio=/.hugetlb=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.pids=/machine.slice/libpod-08491c4650e16a86717dbbdef22866b653cd38fa3cfaed91b7f9829d3b8765a7.scope/container.rdma=/machine.slice.misc=/machine.slice. flags=570472451(CLONE_FILES|CLONE_FS|CLONE_SIGHAND|CLONE_SYSVSEM|CLONE_THREAD|CLONE_VM|CLONE_SETTLS) uid=11 gid=100 vtid=1(systemd) vpid=1(systemd) pidns_init_start_ts=0","evt.category":"process","evt.type":"clone","group.gid":100,"group.name":"users","k8s.ns.name":"","k8s.pod.name":"","proc.cmdline":"http-echo -text=hello","proc.exe":"/http-echo","user.homedir":"/root","user.name":"operator","user.uid":11}
{0x7ffe5260ed60, 0xc}, 0x2)
	/usr/local/go/src/net/url/url.go:331 +0x335
net/url.PathEscape(...)
	/usr/local/go/src/net/url/url.go:283
github.com/containers/podman/v5/pkg/bindings.(*Connection).DoRequest(0xc000059620, {0x7f6d907600d8, 0xc000226690}, {0x0, 0x0}, {0x7f6d9016d3bf, 0x3}, {0x7f6d90181825, 0x13}, 0xc00025e960, ...)
	/go/pkg/mod/github.com/containers/podman/v5@v5.4.1/pkg/bindings/connection.go:393 +0x319
github.com/containers/podman/v5/pkg/bindings/containers.Inspect({0x7f6d907600d8, 0xc000226690}, {0x7ffe5260ed60, 0xc}, 0x0?)
	/go/pkg/mod/github.com/containers/podman/v5@v5.4.1/pkg/bindings/containers/containers.go:119 +0x146
github.com/falcosecurity/plugins/plugins/container/go-worker/pkg/container.(*podmanEngine).get(0xc0000641a0, {0x7f6d90760110?, 0xc0000f4370?}, {0x7ffe5260ed60, 0xc})
	/__w/plugins/plugins/plugins/container/go-worker/pkg/container/podman.go:191 +0xb5
github.com/falcosecurity/plugins/plugins/container/go-worker/pkg/container.(*fetcher).Listen.func1()
	/__w/plugins/plugins/plugins/container/go-worker/pkg/container/fetcher.go:78 +0x1a2
created by github.com/falcosecurity/plugins/plugins/container/go-worker/pkg/container.(*fetcher).Listen in goroutine 52
	/__w/plugins/plugins/plugins/container/go-worker/pkg/container/fetcher.go:65 +0xf5

[FedeDP]

In this call, podman will store into ctx its key/value for the connection, see https://github.com/falcosecurity/plugins/blob/main/plugins/container/go-worker/pkg/container/podman.go#L32 (and NewConnection behavior: https://github.com/containers/podman/blob/main/pkg/bindings/connection.go#L139).

From NewConnection doc:

// NewConnectionWithIdentity takes a URI as a string and returns a context with the
// Connection embedded as a value. This context needs to be passed to each
// endpoint to work correctly.

[github-actions]

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