CLI - Login flow

[bfops]

Description of Changes

Add the spacetime login command, which gets a login token from the web server.

I have removed IdentityConfig in this PR, because we don't want to be storing identities anymore. I've also removed almost all of the --identity CLI parameters, because we want users to be going through spacetime login to switch identities, rather than "just in time" via CLI params.

Closes https://github.com/clockworklabs/SpacetimeDB/issues/1847.

API and ABI breaking changes

This breaks existing stored identities in the config file.

Expected complexity level and risk

3

Testing

• Get a token using spacetime login --host [web-host] (a local one works fine)
• Run a local server and get a token using spacetime login --direct local
• With either token, publish a module, call a function, and print logs.

Future work

• Consider how spacetimedb_token should look to be backwards-compatible with the future changes (e.g. we may want to allow users to login to switch between multiple accounts - what will we cache and where?)
• Move spacetimedb_token out of config so we're no longer storing sensitive tokens in a human-edited file

[bfops]

(Going to fix Internal tests before merging)