podman-compose accepts non-standard type extension for secrets

[ETCaton]

Describe the bug

In the process of implementing #971 it looks like

        - source: my_secret
          target: ENV_SECRET
          type: env

was added to support setting environment variables, however type: is not a standard key for a secret per the Compose spec: https://github.com/compose-spec/compose-spec/blob/main/09-secrets.md.

It should likely be x-type: as it would be a Podman Compose extension (or potentially reverted as it seems Docker Compose has its own workaround to accomplish this already: https://stackoverflow.com/questions/48094850/docker-stack-setting-environment-variable-from-secrets/)

To Reproduce
Steps to reproduce the behavior:
I noticed this while using podlet on a project that used this, but you can trivially replicate as follows:

❯ command -v podlet && git clone "https://github.com/containers/podman-compose" && cd podman-compose/tests/integration/secrets && podlet compose

Expected output (since this refers to secrets not supported by podlet yet)

Error:
   0: error converting compose file
   1: only external `secrets` are supported

Location:
   src/cli/compose.rs:136

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.

Actual output

Error:
   0: error converting compose file
   1: error reading compose file
   2: File `docker-compose.yaml` is not a valid compose file
   3: services.test.secrets[7]: extension key `type` does not start with "x-" at line 34 column 11

Location:
   src/cli/compose.rs:203

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.

Environment:

• OS: Mac
• podman-compose version 1.2.0
• podman version 5.3.1
• podlet version: 0.3.0