The regal fix command should explain which violations are fixable

[anderseknert]

The regal fix command should inform the user of what fixes it may apply before the command is run, as it's currently not clear what the impact of running the command might be. We'll probably want to say something like:

Fix Rego source files with linter violations. Note that this command is intended to help
fix style-related issues, and could be considered as a stricter `opa-fmt` command.
Issues like bugs should be fixed manually, as it is important to understand why the
were flagged. The linter rules with automatic fixes available are currently:

- opa-fmt
- use-rego-v1
- ...
- ...

It would also be helpful if we updated the docs for each rule where a fix is available with a note saying it's so. Perhaps in the header where we already provide things like name and category.

Current output of running regal fix --help:

Fix Rego source files with linter violations.

Usage:
  main fix <path> [path [...]] [flags]

Flags:
  -c, --config-file string        set path of configuration file
      --debug                     enable debug logging (including print output from custom policy)
  -d, --disable string            disable specific rule(s). This flag can be repeated.
  -D, --disable-all               disable all rules
      --disable-category string   disable all rules in a category. This flag can be repeated.
  -e, --enable string             enable specific rule(s). This flag can be repeated.
  -E, --enable-all                enable all rules
      --enable-category string    enable all rules in a category. This flag can be repeated.
  -f, --format string             set output format (pretty is the only supported format) (default "pretty")
  -h, --help                      help for fix
      --ignore-files string       ignore all files matching a glob-pattern. This flag can be repeated.
      --no-color                  Disable color output
  -o, --output-file string        set file to use for fixing output, defaults to stdout
      --pprof string              enable profiling (must be one of cpu, clock, mem_heap, mem_allocs, trace, goroutine, mutex, block, thread_creation)
  -r, --rules string              set custom rules file(s). This flag can be repeated.
      --timeout duration          set timeout for fixing (default unlimited)