fix(sqlcon): Parse DSN manually instead of using url.Parse

[kaorimatz]

Related issue

ory/keto#145

Proposed changes

Parse a DSN string manually instead of using url.Parse since a DSN string for MySQL is no longer always parsable with url.Parse after this change (Ref: golang/go#33646).

$ cat <<EOF > main.go
package main

import (
        "fmt"
        "net/url"
)

func main() {
        fmt.Println(url.Parse("mysql://tcp(127.0.0.1:3306)/"))
}
EOF
$ go version
go version go1.14 darwin/amd64
$ go run main.go
<nil> parse "mysql://tcp(127.0.0.1:3306)/": invalid port ":3306)" after host

Checklist

• I have read the contributing guidelines
• I have read the security policy
• I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security
  vulnerability, I confirm that I got green light (please contact security@ory.sh) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation within the code base (if appropriate)

Further comments

I have only tested this with keto migrate sql.

[claassistantio]

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