Config schema definition of graphql server and exported config doesn't match

We have an exported config that looks like this:

```
langcode: en
status: true
dependencies: { }
name: thunder_graphql
label: 'Thunder - GraphQL Server'
schema: composable
schema_configuration:
composable:
extensions:
thunder_paragraphs: thunder_paragraphs
thunder_media: thunder_media
thunder_routing: thunder_routing
thunder_pages: thunder_pages
persisted_queries_settings: { }
endpoint: /graphql
debug_flag: 0
caching: true
batching: true
```

There are two problems with this config:

1. The `schema_configuration` doesn't match the schema definition

```
schema_configuration:
type: 'graphql.schema.[%parent.schema]'
```
The schema definition needs to be this to match::
```
schema_configuration:
type: mapping
label: 'Schema config'
mapping:
composable:
label: Composable schema
type: graphql.schema.composable
```
Or the exported config structure has to change.

2. The sequence in `graphql.schema.composable` is defined as boolean but it's exported as strings
```
schema_configuration:
composable:
extensions:
thunder_paragraphs: thunder_paragraphs
thunder_media: thunder_media
thunder_routing: thunder_routing
thunder_pages: thunder_pages
```

I think that should be changed to
```
schema_configuration:
composable:
extensions:
thunder_paragraphs: true
thunder_media: true
thunder_routing: true
thunder_pages: true
```