Dynamic mode indexes may have spaces in the names, but strict indexes can't

Describe the bug

I try to create two indexes, one like

version: 0.7
index_id: sales-schemaless
doc_mapping:
  mode: dynamic
indexing_settings:
  commit_timeout_secs: 30

and one like

version: 0.7
index_id: sales-schema
doc_mapping:
  mode: strict
  timestamp_field: "Order Date"
  field_mappings:
    - name: Order Date
      type: datetime
      input_formats:
        - iso8601
      fast: true
    - name: "Ship Date"
      type: datetime
      input_formats:
        - iso8601
      fast: true
    - name: "Country"
      type: text
indexing_settings:
 commit_timeout_secs: 30

the second one won't create with the message;

./quickwit index create --index-config sales_schema_config.yaml
❯ Creating index...
✘ command failed: API error: (code=400 Bad Request, message=invalid config: failed to parse YAML file: field name `Order Date` contains illegal characters. field names must only contain uppercase and lowercase ASCII letters, digits, hyphens `-`, periods `.`, and underscores `_`)

Caused by:
    (code=400 Bad Request, message=invalid config: failed to parse YAML file: field name `Order Date` contains illegal characters. field names must only contain uppercase and lowercase ASCII letters, digits, hyphens `-`, periods `.`, and underscores `_`)

but the first one will create and actually work with a jsonl that has spaces in the keys! So i can't force a schema on a data set that works if the schema is dynamic.

Steps to reproduce (if applicable)
Steps to reproduce the behavior:

1. create the schemas above
   2.insert the following data into the dynamic schema

{"Country":"Azerbaijan","Order Date":"2014-10-08T00:00:00+00:00","Ship Date":"2014-10-23T00:00:00+00:00"}

with the command

./quickwit tool local-ingest --index sales-schemaless --input-path

3. observe that it works :)
4. try to create the second schema
5. observe it doesn't work

Expected behavior

I'd expect the strict schemas to be able to emulate the dynamic schemas

Configuration:
Please provide:

1. Output of quickwit --version

Quickwit 0.8.0 (aarch64-unknown-linux-gnu 2024-03-18T15:20:23Z 7af4596)

2. The index_config.yaml

see above^^^

Start with the index_config.yaml examples and reproduce the behavior through quickwit index create, then compare strict field-name validation with dynamic indexing via quickwit tool local-ingest. Done means a strict schema can accept the same space-containing JSONL keys as the dynamic schema, with coverage for the reproduced configurations.