feat: add MarkFlagsMutuallyExclusiveAndRequired

[baruchiro]

Fixes #1216

I chose the most naive way.

Just like the flow of mutuallyExclusive, I cloned it to another flow for mutuallyExclusiveAndRequired, with only different condition, to return an error also if the set slice is empty.

Example:

❯ go run .
Error: exactly one of the flags in the group [op1 op2] must be set; none were set
Usage:
  cobra-temp [flags]

Flags:
  -h, --help         help for cobra-temp
      --op1 string   Option1 mutually exclusive and required with Option2
      --op2 string   Option2 mutually exclusive and required with Option1

exit status 1
❯ go run . --op1 foo
❯ go run . --op2 foo
❯ go run . --op1 foo --op2 foo
Error: exactly one of the flags in the group [op1 op2] must be set; [op1 op2] were all set
Usage:
  cobra-temp [flags]

Flags:
  -h, --help         help for cobra-temp
      --op1 string   Option1 mutually exclusive and required with Option2
      --op2 string   Option2 mutually exclusive and required with Option1

exit status 1

[CLAassistant]

All committers have signed the CLA.

[marckhouzam]

Thanks @baruchiro !
The issue this PR fixes has a long discussion.
Could you add in the description of this PR an example of how this new group can be used?

[baruchiro]

@marckhouzam Description updated

[marckhouzam]

@marckhouzam Description updated

Thanks. Now that understand better what this does I think it overlaps with #1952 which allows to require one flag out of a group and then use the existing API MarkFlagsMutuallyExclusive to force mutual exclusiveness.

What do you think?

[baruchiro]

I think #1952 is better, thanks!