schema-ast should pull deprecation notices about enums

**Is your feature request related to a problem? Please describe.**

If the origin schema has deprecated members of enums (e.g. below), then it should be reflected in the generated schema.

```graphql
enum BasicOpportunityPositionType {
CONTRACT @deprecated(reason: "Use LONG_TERM and SHORT_TERM instead.")
FULL_TIME @deprecated(reason: "Use LONG_TERM and SHORT_TERM instead.")
INTERNSHIP @deprecated(reason: "Use LONG_TERM and SHORT_TERM instead.")
LONG_TERM
PART_TIME @deprecated(reason: "Use LONG_TERM and SHORT_TERM instead.")
SHORT_TERM
}
```

Currently, deprecations are not reflected in the schema:

```graphql
enum BasicOpportunityPositionType {
CONTRACT
FULL_TIME
INTERNSHIP
LONG_TERM
PART_TIME
SHORT_TERM
}
```