bug(connectors): meilisearch_sink URL scheme check is case-sensitive, silently connects to the wrong host

### Description

`meilisearch_sink::normalize_host` detects the URL scheme via `trimmed.starts_with("http://") || trimmed.starts_with("https://")`, which is case-sensitive. A config value like `HTTPS://realhost:9200` matches neither literal, falls through to the "no scheme" branch, and gets `http://` prepended, producing `http://HTTPS://realhost:9200`.

### Affected area / component

Connectors

### Proposed solution

Detect the scheme case-insensitively (e.g. `eq_ignore_ascii_case` on the split-off scheme) instead of a literal `starts_with` check.

### Alternatives considered

_No response_

### Contribution

- [x] I'm willing to submit a pull request to implement this feature

### Good first issue

- [ ] I think this could be a good first issue for a new contributor