Feature Request: support SubstringComparator with NOT_EQUAL

We are refactoring the application with Cloud Bigtable from HBase.

The code snippet using HBase:

```
if (StringUtils.isNotBlank(value)) {
SubstringComparator notContainsValue = new SubstringComparator(value);
SingleColumnValueFilter filter = new SingleColumnValueFilter(CF, Bytes.toBytes(CQ1),
CompareFilter.CompareOp.NOT_EQUAL, notContainsValue);
filterList.addFilter(filter);
}
```

However, Bigtable's HBase API does not support SubstringComparator with NOT_EQUAL. And we got the following error:

```
reason='ValueFilter must have either a BinaryComparator with any compareOp or a RegexStringComparator with an EQUAL compareOp. Found (SubstringComparator, NOT_EQUAL)'}
```