Automatic merge from submit-queue
Allow specifying secret data using strings
This PR allows specifying non-binary data values in `Secret` objects as `"stringData":{"key":"string value"}`, in addition to the existing base64 []byte serializations in the `data` field.
On write, the keys and values in the `stringData` field are merged to the `data` map, overwriting any values already present in the `data` map. The move is one-way, the `stringData` field is never output when reading from the API.
A Secret could be created like this:
```
{
"kind":"Secret",
"apiVersion":"v1",
"metadata":{"name":"mysecret"},
"data":{
"image":"<base64-encoded-jpg>"
},
"stringData":{
"username": "myuser",
"password": "mypassword"
}
}
```
and when read from the API would look like this:
```
{
"kind":"Secret",
"apiVersion":"v1",
"metadata":{"name":"mysecret",...},
"data":{
"image":"<base64-encoded-jpg>"
"username": "bXl1c2Vy",
"password": "bXlwYXNzd29yZA=="
}
}
```