Change summary

This PR adds the 'service purge' command as a replacement for the 'purge' command. The 'purge' command is still available as an alias, but will issue a deprecation warning when it is used.

This involved a number of changes:

1. The existing 'pkg/commands/purge' package content was moved to 'pkg/commands/service/purge', and modified to work as expected in that location.
2. A new 'pkg/commands/alias' package was added to hold alias-only packages.
3. An alias was added in 'pkg/commands/alias/purge'. This alias uses struct embedding to avoid duplicating any of the code from the `pkg/commands/service/purge' package. The alias command is 'unlisted' and issues a deprecation warning when it is used.

This PR also fixes the make fmt target in the Makefile to work properly.

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User Impact

New deprecation warning for the purge command.