bug: `import-url` drops secret and breaks URL if secret resembles a boolean

### Describe the bug

When using the `import-url` command with a URL that includes a `primary` flag and a `secret`, the internal `parseImportURLArg` logic splits the string by `:` and searches backward for the boolean flag. If the provided secret is a string that parses as a boolean (e.g. `true`, `false`, `1`, `0`), the parser incorrectly consumes the secret as the `primary` flag.

### Expected behavior

The command should correctly parse the URL, the boolean `primary` flag, and the `secret` string, even if the secret text happens to resemble a boolean value.

### Actual behavior

The secret is dropped entirely, the boolean `primary` flag is ignored, and the parsed URL incorrectly retains the boolean string at the end, causing the import to fail.

### How to Reproduce?

Reproducer:
1. Run a dry run or import using a boolean-like secret:
`microcks import-url "http://example.com/api:true:false"`
2. Observe that the logic parses the URL as `http://example.com/api:true`, the primary flag as `false`, and the secret as empty.

### Microcks version or git rev

`main` (Latest)

### Install method (`docker-compose`, `helm chart`, `operator`, `docker-desktop extension`,...)

CLI

### Additional information

This is a great `good first issue` to refactor the `parseImportURLArg` function in `cmd/importURL.go` to safely separate the URL, flag, and secret without relying on backward boolean parsing.

Start in cmd/importURL.go and inspect parseImportURLArg, then reproduce the issue with `microcks import-url "http://example.com/api:true:false"`. Ensure the parser preserves the URL, primary flag, and boolean-like secret, and verify the dry run or import no longer drops the secret or corrupts the URL.

Written by the indexing model from the issue text.