This replaces all usages of gopkg.in/yaml.v2 by v3 everywhere, adapts
the UnmarshalYAML methods to the new signature, and replaces the
UnmarshalStrict calls by the decoder with KnownFields flag.

util.YAMLMarshalUnmarshal doesn't work because it doesn't support
unmarshaling map[interface{}]interface{}

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

yaml.v3 can't unmarshal to map[interface{}]interface{},
but actually map[string]interface{} should be enough.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

This commit is the latest v3 with
go-yaml/yaml#691 cherry-picked on top of it, to
provide support for strict unmarshaling when doing custom unmarshaling
(see go-yaml/yaml#460)

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

There's no such field as
`alertmanager_notification_limits_per_integration`
and the fixed strict parsing has detected this.

How does this test pass in `main`?

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

gopkg.in/yaml.v3 implementation doesn't seem to set the entire value to
zero value if an empty node is specified in the YAML. So we don't need
that check again, and we can adapt the test just to check that this
assertion is true.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>