spacetime server add - Remove trailing /s from server URIs

[bfops]

Description of Changes

Fixes part of #1551. See the issue for more background details.

API and ABI breaking changes

No. Un-breaks some cases.

Expected complexity level and risk

1

Testing

Before:

$ spacetime server add https://testnet.spacetimedb.com/ testnet-test
Error: Unable to retrieve fingerprint for server: https://testnet.spacetimedb.com/
Is the server running?
Add a server without retrieving its fingerprint with:
	spacetime server add https://testnet.spacetimedb.com/ --no-fingerprint

Caused by:
    HTTP status client error (404 Not Found) for url (https://testnet.spacetimedb.com//identity/public-key)

On this branch:

$ cargo run -- server add https://testnet.spacetimedb.com/ testnet-test
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
     Running `target/debug/spacetime server add 'https://testnet.spacetimedb.com/' testnet-test`
For server https://testnet.spacetimedb.com, got fingerprint:
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEmF4e1ygt1sgluqRmi1Lwz8jK+GVz
kUnUtZJsDu5ACsJqwSDiMMDnBrNW41Bx0Qrg8FJNsK7mC767nvVmSYzyDg==
-----END PUBLIC KEY-----

Error: Server already configured for host: testnet.spacetimedb.com

[jdetter]

Looks good to me, I haven't tested it but I agree with the change.

Thanks Zeke! 👍