Update old references to Inbucket with Mailpit

[Dakota-Schramm]

Describe the bug
The config.toml file still refers to inbucket as the local development server when it should be Mailpit.

To Reproduce
Steps to reproduce the behavior:

1. Create a new supabase cli setup
2. See the generated config.toml file with incorrect references

Expected behavior
References should be updated

Screenshots
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Additional context
If applicable, add any other context about the problem here.

• Version of supabase-cli: 2.98.2

[avallete]

True, I think the actual config should not contains implementation reference (such as inbucket/mailpit).

Maybe something like "local_smtp" so if implementation change, the value doesn't.

Changing this would also be a breaking change, so I think we need to phase it into:

1. Updating the config but keeping both values as valid (inbucket/local_smtp), showing a warning to migrate to the new preferred option. Updating the template to the new default for new config going forward.
2. Eventually we'll make a final switch into a breaking change once thing has settled.