Parse credentials as map[string]any{}

[turkenh]

Description of your changes

Currently, it is not possible to use a credential value other than string in ProviderConfig.

Using the following provider config secret, fails with the following error:

apiVersion: v1
kind: Secret
metadata:
  name: vault-creds
  namespace: vault
type: Opaque
stringData:
  # WARNING: DO NOT CHECK REAL TOKENS INTO GIT
  credentials: |
    {"auth_login":{"path":"auth/approle/login","namespace":"NAMESPACE","parameters":{"role_id":"ROLE_ID","secret_id":"SECRET_ID"}}}

2023-08-10T08:50:43Z	DEBUG	events	cannot get terraform setup: cannot unmarshal vault credentials as JSON: json: cannot unmarshal object into Go value of type string	{"type": "Warning", "object": {"kind":"Mount","name":"kv-v2-secret-mount","uid":"8ea6a132-c6cf-49c9-83d3-

This PR fixes credential parsing by using map[string]any{} as it type.
I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

To be tested, built provider image turkenh/provider-vault:v0.0.0-50.g8d5443d from this PR.

[linuxbsdfreak]

Tested the change and it works.

[haarchri]

LGTM