Small quality of life updates for AMQPConnectionConfiguration

[xtremekforever]

We have started working with this library to test migrating some applications from C# to Swift, and noticed a few things that could be improved in the library when related to the AMQPConnectionConfiguration. Hopefully this can be helpful and included as a small improvement.

• Add .lowercased() to check for "%2f" string as a URL encoded "/" character. Connection strings can come with an uppercase "%2F" and this is completely valid as well.
• Add tls optional parameter for constructors to allow the user of the library to easily provide a custom TLSConfiguration.

[funcmike]

Nice to hear about more users of library :). Pull request looks good, thanks for Your contribution.