feat(crypto): support md5 plain for imported password hashes (#8189)

# Which Problems Are Solved

Allow verification of imported passwords hashed with plain md5, without
salt. These are password digests typically created by one of:

- `printf "password" | md5sum` on most linux systems.
- PHP's `md5("password")`
- Python3's `hashlib.md5(b"password").hexdigest()`

# How the Problems Are Solved

- Upgrade passwap to
[v0.6.0](https://github.com/zitadel/passwap/releases/tag/v0.6.0)
- Add md5plain as a new verfier option in `defaults.yaml`

# Additional Changes

- Updated documentation to explain difference between `md5` (crypt) and
`md5plain` verifiers.

# Additional Context

- Requested by customer for import case

go.sum

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