feat(cli): cobra cli args library to support negation [no-] flags

[ivankatliarchuk]

What does it do ?

• At the moment default cli is Kingpin. Cobra is hidden behind feature flag

  external-dns/pkg/apis/externaldns/types.go

  Line 502 in 690259f

  if strings.HasPrefix(a, "--cli-backend") {

  no risks to fix/modify things
• Currently cobra library does not support negation [no-] flags. Added wrapper for that.
• I was thinking to add support to actual library, from first look not straightforward Support Boolean flags with only NoOptDefVal, no --foo=true syntax. spf13/pflag#214

Follow-ups:

• when --help generate similar output as for kingpin but for cobra, aka add --[no-]aws-zone-match-parent kind of ouput
• Generate flags from Cobra. As currently they generated from kingpin

  external-dns/internal/gen/docs/flags/main.go

  Line 65 in 690259f

  app := cfg.App(&cfg.Config{})

• Deprecate completely kingpin library feat(cli): deprecate kingpin #6024

Motivation

Follow-up for #5836

Relates #5379

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

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[coveralls]

Pull Request Test Coverage Report for Build 20211224035

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 9 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.06%) to 78.636%

---

Files with Coverage Reduction	New Missed Lines	%
apis/externaldns/types.go	3	99.13%
apis/externaldns/binders.go	6	94.39%

Totals
Change from base Build 20209428653:	-0.06%
Covered Lines:	16056
Relevant Lines:	20418

---

💛 - Coveralls

[mloiseleur]

@ivankatliarchuk 🤔 Why introduce such complexity ?

I mean,

• Only syntax like --xxx=true|false => ✅
• Only syntax like --xxx|--no-xxx => ✅
• Both syntax: (--xxx=true|false)|(--no-xxx=true|false) => 😵‍💫

We may also introduce a breaking change, where users need to switch their flags from current --xxx|--no-xxx (kingpin) to --xxx=true|false (cobra). Wdyt ?

[ivankatliarchuk]

Agree it adds a bit of complexity. One of the ideas is to keep behaviour as is, and move flag changes to upstream library at some point, if they accept changes.

If we going to move away from negative flags - yes it will simplify things for us. For users, semantics is going to change for every boolean flag. Like they need to explicitly specify true|false. Nothing wrong with this approach.

I leave it for reviewer to decide.