Misleading statements in mergeOptions

### URL

https://docs.crossplane.io/latest/concepts/patch-and-transform/#merge-options

### What's Wrong?

According to the documentation:

> With an object, use keepMapValues: true to leave existing object keys in tact. The patch updates any matching keys between the input and destination data.

The second sentence suggests that a patch changing existing keys (or updating them!) will update them, while apparently that's not the case as discussed with Upbound support.

Given this param for a composition:

```
spec:
params:
clusterName: main
tags:
component: cluster
country: us
foo: baz
```

An MR containing:

```
spec:
forProvider:
tags:
foo: bar
```

and being applied a patch like:

```
- type: FromCompositeFieldPath
fromFieldPath: spec.parameters.clusterName
toFieldPath: spec.forProvider.tags.cluster-name
- type: FromCompositeFieldPath
fromFieldPath: spec.parameters.tags
toFieldPath: spec.forProvider.tags
policy:
mergeOptions:
keepMapValues: true
```

will update the tags for the MR and get:

```
tags:
cluster-name: main
component: eks
country: us
foo: bar
```

which is correct, according to documentation.

*However* updating the parameters to:

```
spec:
params:
clusterName: main
tags:
component: network # updated
country: es # updated
foo: baz
```

does not reflect into any changes in the MR, while according to the documentation:

> [...] The patch updates any matching keys between the input and destination data.

and the following was expected in the MR:

```
tags:
cluster-name: main
component: network
country: es
foo: bar
```