silk-datastore-syncer: fix assignment to entry in nil map in Metadata field

[gmllt]

Trying to fix panic assignment to entry in nil map in silk-datastore-syncer code.

When unmarshalling container infos in corresponding struct datastore.Container, Metadata map isn't always instantiated, resulting in a panic error when silk-datastore-syncer tries to store a log_config entry into it.

The panic encountered using v3.30.0 (same on v3.39.0) :

panic: assignment to entry in nil map

goroutine 1 [running]:
main.main()
/var/vcap/data/compile/silk-datastore-syncer/src/code.cloudfoundry.org/silk-datastore-syncer/main.go:106 +0xf52

[MarcPaquette]

Hi @gmllt
Would it be possible to devise a test case for this code change?
Thanks,
@MarcPaquette

[linux-foundation-easycla]

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• ✅ login: gmllt / name: Gilles Miraillet (5fb7a3f, 5dbde8f)

[gmllt]

@MarcPaquette, I've added a test.

[MarcPaquette]

Thanks for the contribution @gmllt !