[incubator/monochart] Dockercfg name mismatch

## Environment
Chart: incubator/monochart v0.25.0

## What I expect

If I use the following in values.yaml

```
dockercfg:
enabled: true
image:
pullSecret:
registry: foo
username: bar
password: baz
...
```

A secret is created and referenced correctly in a Deployment's pullSecrets

## What I experienced

If, for example, my release name is `foo`, the secret is named `foo-dockercfg` but the imagePullSecrets section in the deployment says

```
imagePullSecrets:
- name: foo-monochart
```

Since they don't match, the image pull fails.

## Visual Aids

-
-
-
-