Support enumerating platforms for a extension

[zeroSteiner]

This allows enumerating the platforms (build tuples) that a particular extension has built binaries for. This is foundational work for Metasploit to be able to identify which Meterpreters a particular extension is available for.

Testing Steps

• Install the gem locally.
• Start msfconsole and then load IRB.
• Run MetasploitPayloads::Mettle.available_platforms('sniffer')
  • The sniffer and stdapi extensions are the only ones that Mettle provides. The stdapi is a special case though that's baked into Mettle. It's technically present even if it's not backed by files on disk.
• See a list of platforms where the sniffer extension is available.

Example

>> MetasploitPayloads::Mettle.available_platforms('sniffer')
=> 
["mips64-linux-muslsf",
 "mipsel-linux-muslsf",
 "powerpc64le-linux-musl",
 "mips-linux-muslsf",
 "powerpc-linux-muslsf",
 "s390x-linux-musl",
 "x86_64-linux-musl",
 "i486-linux-musl",
 "armv5l-linux-musleabi",
 "aarch64-linux-musl",
 "armv5b-linux-musleabi",
 "powerpc-e500v2-linux-musl"]
>> MetasploitPayloads::Mettle.available_extensions('x86_64-linux-musl')
=> ["sniffer", "stdapi"]
>> 

[gwillcox-r7]

Some minor comments but overall this looks good to go

[gwillcox-r7]

Looks like this is working well:

msf6 > irb
[*] Starting IRB shell...
[*] You are in the "framework" object

>> MetasploitPayloads::Mettle.available_platforms('sniffer')
=> 
["powerpc-linux-muslsf",
 "mips64-linux-muslsf",
 "armv5b-linux-musleabi",
 "i486-linux-musl",
 "x86_64-linux-musl",
 "s390x-linux-musl",
 "mips-linux-muslsf",
 "powerpc-e500v2-linux-musl",
 "arm-iphone-darwin",
 "powerpc64le-linux-musl",
 "mipsel-linux-muslsf",
 "x86_64-apple-darwin",
 "aarch64-linux-musl",
 "aarch64-iphone-darwin",
 "armv5l-linux-musleabi"]
>>  MetasploitPayloads::Mettle.available_extensions('x86_64-linux-musl')
=> ["sniffer", "stdapi"]
>>