[swagger] List all buckets offset parameter

We should either remove the `offset` parameter from the swagger doc for `GET /buckets` endpoint or put a description for how this parameter is supposed to be used.
```
/buckets:
get:
operationId: GetBuckets
tags:
- Buckets
summary: List all buckets
parameters:
- $ref: '#/components/parameters/TraceSpan'
- $ref: "#/components/parameters/Offset"
- $ref: "#/components/parameters/Limit"
- in: query
name: org
description: The organization name.
schema:
type: string
- in: query
name: orgID
description: The organization ID.
schema:
type: string
- in: query
name: name
description: Only returns buckets with a specific name.
schema:
type: string
```

```
parameters:
Offset:
in: query
name: offset
required: false
schema:
type: integer
minimum: 0
```

Search the Swagger definition for GET /buckets and the shared Offset parameter. Confirm whether offset is supported; done when the specification either removes it from this endpoint or documents how it is used.

Written by the indexing model from the issue text.