Add password credential CLI command

[bgajjala8]

Add CLI support for password credentials :

• Generating password_credentials.gen.go CLI framework
• Implementing password_funcs.go with password-specific flags
• Registering create/update commands in CLI router

This enables password credentials through the CLI:

• boundary credentials create password
• boundary credentials update password

[bgajjala8]

@laero We will hold from merging this PR until API and Repository changes are complete.

[louisruch]

Would be good to add a bats test to this, see https://github.com/hashicorp/boundary/blob/main/internal/tests/cli/boundary/credentials.bats
Note that as you mentioned until the API/domain changes are complete that test wont do much

[bgajjala8]

Would be good to add a bats test to this, see https://github.com/hashicorp/boundary/blob/main/internal/tests/cli/boundary/credentials.bats Note that as you mentioned until the API/domain changes are complete that test wont do much

@louisruch Yep! I can make these test additions as part of this PR

[bgajjala8]

@laero I added credential bats tests and added unimplemented message to the credential service. This will fail when running the bats test until the service implementation is completed. Should we go ahead with reviewing and getting this part in now that we have some testing in place?

cc: @louisruch