elastic: Create the metadata-fetcher secret to all namespaces

Currently only the loaders git really use it but they all need to mount the secret
volume (since it's using the same declaration). So it needs to be present in all
namespaces [1].

[1]
```
for TYPE in git bzr cvs maven pypi npm svn; do; kubectl apply -f loaders-metadata-fetcher.secret.yaml --namespace ns-loaders-$TYPE; done
secret/metadata-fetcher-credentials configured
secret/metadata-fetcher-credentials created
secret/metadata-fetcher-credentials created
secret/metadata-fetcher-credentials created
secret/metadata-fetcher-credentials created
secret/metadata-fetcher-credentials created
secret/metadata-fetcher-credentials created
```

Related to T4144