QuotaVersion/ResourceVersion lose their chain fields on JSON marshal (promoted MarshalJSON)

[rchildress87]

store.QuotaVersion embeds store.Quota, and Quota declares a
value-receiver MarshalJSON. Go promotes that method to the embedding
struct, and QuotaVersion declares none of its own — so json.Marshal of a
QuotaVersion emits only the Quota wire shape and silently drops every field
the version type adds.

Reproduction:

v := store.QuotaVersion{
    Quota:        store.Quota{ID: "abc", Provider: "aws", Name: "n"},
    RootID:       "abc",
    VersionRowID: "0197f0a2-1c3d-7e00-9a1b-2c3d4e5f6a7b",
    SupersededBy: &sup,
}
b, _ := json.Marshal(v)

Output — no rootId, no versionRowId, no supersededBy:

{"id":"abc","provider":"aws","accountId":"","accountName":null,"region":"",
 "serviceCode":"","serviceName":null,"quotaCode":"","name":"n",
 "description":null,"unit":null,"value":null,"defaultValue":null,
 "adjustable":false,"globalQuota":false,"appliedLevel":null,
 "discoveredAt":"","discoveredBy":"","attributes":{}}

Six fields are lost: versionRowId, rootId, previousVersionId,
supersededBy, verifiedAt, verifiedBy.

This matters most for the version chain, which is the reason the separate
quotas table keeps history at all. Without supersededBy a consumer cannot
tell which row is current, and without previousVersionId the chain cannot be
ordered except by discoveredAt. Any JSON output of GetQuotaVersions is
affected — disco history for a quota, and any downstream consumer.

store.ResourceVersion has the identical defect for the same reason, so a fix
should probably cover both rather than just this one.

Suggested fix: give QuotaVersion (and ResourceVersion) its own
MarshalJSON that starts from the embedded type's output and adds the chain
fields, rather than relying on promotion.

disco-saas currently works around this by assembling the wire object itself
(marshalQuotaVersion in internal/http/v1_quota_handlers.go), guarded by a
test that logs when the workaround becomes redundant. That wrapper can be
deleted once this is fixed.