bbctl configuration values that can only be certain values should use enums

Configuration values that can only be a specific value should be converted to use custom types instead of generic values like string.

For example:

// Log format: json, text
LogFormat string `mapstructure:"bbctl-log-format" json:"bbctl-log-format" yaml:"bbctl-log-format"`

can only be one of two values, so a custom type with constants should be created:

type LogFormat string 

const (
    Text LogFormat = "text"
    JSON LogFormat = "json"
)

The global configuration can then be updated to:

// Log format: json, text
LogFormat LogFormat `mapstructure:"bbctl-log-format" json:"bbctl-log-format" yaml:"bbctl-log-format"`

These values are still functionally strings and can be worked with as such, but this way the compiler can assert that only valid values are set.

Acceptance Criteria

• Audit all configuration fields (top level and sub) and identify what needs to be updated
• Create types for all valid fields
• Sync with @nbazzeghin on big-bang&488 for anything that will be updated so he can return the correct types.