fix(deps): update module github.com/knadh/koanf/v2 to v2.1.0 (#31061)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [github.com/knadh/koanf/v2](https://togithub.com/knadh/koanf) |
`v2.0.2` -> `v2.1.0` |
[![age](https://developer.mend.io/api/mc/badges/age/go/github.com%2fknadh%2fkoanf%2fv2/v2.1.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/go/github.com%2fknadh%2fkoanf%2fv2/v2.1.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/go/github.com%2fknadh%2fkoanf%2fv2/v2.0.2/v2.1.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/go/github.com%2fknadh%2fkoanf%2fv2/v2.0.2/v2.1.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>knadh/koanf (github.com/knadh/koanf/v2)</summary>

### [`v2.1.0`](https://togithub.com/knadh/koanf/releases/tag/v2.1.0)

[Compare
Source](https://togithub.com/knadh/koanf/compare/v2.0.2...v2.1.0)

### Important


[https://github.com/mitchellh/mapstructure/issues/349#issuecomment-1860372162](https://togithub.com/mitchellh/mapstructure/issues/349#issuecomment-1860372162)
is discontinued and koanf has switched to using the fork
`github.com/go-viper/mapstructure/v2`.

If you are referencing the mapstructure lib in your code (custom
DecoderConfig), you have to switch the paths to the above forked version
of koanf.

`github.com/mitchellh/mapstructure` =>
`github.com/go-viper/mapstructure/v2`

#### What's Changed

- fix: retract v2.0.2 by [@&#8203;rhnvrm](https://togithub.com/rhnvrm)
in
[https://github.com/knadh/koanf/pull/270](https://togithub.com/knadh/koanf/pull/270)

**Full Changelog**:
knadh/koanf@v2.0.2...v2.1.0

</details>

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cmd/opampsupervisor/go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/knadh/koanf/parsers/yaml v0.1.0
 	github.com/knadh/koanf/providers/file v0.1.0
 	github.com/knadh/koanf/providers/rawbytes v0.1.0
-	github.com/knadh/koanf/v2 v2.0.2
+	github.com/knadh/koanf/v2 v2.1.0
 	github.com/oklog/ulid/v2 v2.1.0
 	github.com/open-telemetry/opamp-go v0.12.0
 	github.com/stretchr/testify v1.8.4