add ssconf support

[pmoieni]

this PR adds support for ssconf transport URL to Outline CLI. I was not sure what to do with the prefix field so just left it untouched. I was not able to test the implementation either.

OutlineVPN CLI (experimental)
[INFO] 2024/08/25 15:12:11 updated global IPv6 support: false
[INFO] 2024/08/25 15:12:11 updated global IPv6 support: true
[ERROR] 2024/08/25 15:12:11 failed to create OutlineDevice: failed to create TCP dialer: failed to decode host string [ss:///redacted/@/redacted/:8080]: illegal base64 data at input byte 2

using the official access keys I get the above error.
no such issue while using ssconf key:

OutlineVPN CLI (experimental)
[INFO] 2024/08/25 15:58:38 updated global IPv6 support: false
[INFO] 2024/08/25 15:58:41 remote server cannot handle UDP traffic, switch to DNS truncate mode.
[INFO] 2024/08/25 15:58:41 routing traffic from 10.233.233.1 to 10.233.233.2/32 through nic 9
[INFO] 2024/08/25 15:58:41 routing traffic via gw 10.233.233.2 through nic 9...
[INFO] 2024/08/25 15:58:41 ip rule 'from all not to /redacted/ via table 233' created

but it doesn't seem to establish any kind of connection at all

OS: OpenSuse Tumbleweed

[google-cla]

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[jyyi1]

Thanks so much for this PR! We're currently migrating dynamic key feature into Go in Outline Client as well. To ensure the best integration, we'd appreciate a bit more time to review your PR and explore potential code sharing opportunities.

[pmoieni]

@jyyi1 looking forward to that, ready to improve the code if necessary.