chore(cli): create 'gateway' subcommand for network commands

[Tieske]

This introduces the gateway sub-command, and moves the existing commands under the new sub-command. Since aliases are in place this is non-breaking.

The old commands will now display a deprecation warning.

New structure:

- version     Print the decK version
- completion  Generate completion script
- help        Help about any command
​
- file        decK file operations
  - add-tags     Adds tags to objects in a decK file
  - list-tags    Lists current tags to objects in a decK file
  - merge        Merges multiple decK files into one
  - openapi2kong Convert OpenAPI files to Kong's decK format
  - patch        Applies patches on top of a decK file
  - remove-tags  Removes tags from objects in a decK file
  - convert      Convert files from one format into another format
  - render       renders a final decK file as it would be synced (for local diffs)
  - validate     Validate the state file (locally)
- gateway     online operations
  - diff         Diff the current entities in Kong with the one on disks
  - dump         Export Kong configuration to a file
  - ping         Verify connectivity with Kong
  - reset        Reset deletes all entities in Kong
  - sync         Sync performs operations to get Kong's configuration to match the state file
  - validate     Validate the state file (online)
- diff        ==> alias for backward compatibilty
- dump        ==> alias for backward compatibilty
- ping        ==> alias for backward compatibilty
- reset       ==> alias for backward compatibilty
- sync        ==> alias for backward compatibilty
- validate    ==> alias for backward compatibilty
- convert     ==> alias for backward compatibilty

Todo:

• create "kong" subcommand
• move kong commands under "kong"
• change defaults of "kong xxx" commands to focus on stdin/stdout
• change "kong" subcommand to "gateway", see internal discussion
• add file validate which was removed by chore(validate): remove validate again from file subcommand #971

Jira: APIOPS-98

[codecov-commenter]

Codecov Report

Attention: 548 lines in your changes are missing coverage. Please review.

Comparison is base (94c197b) 33.18% compared to head (33abcc8) 32.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #962      +/-   ##
==========================================
- Coverage   33.18%   32.75%   -0.43%     
==========================================
  Files         102      103       +1     
  Lines       12582    12746     +164     
==========================================
  Hits         4175     4175              
- Misses       8000     8164     +164     
  Partials      407      407              

Files	Coverage Δ
cmd/konnect.go	0.00% <0.00%> (ø)
cmd/file.go	0.00% <0.00%> (ø)
cmd/gateway.go	0.00% <0.00%> (ø)
cmd/file_convert.go	0.00% <0.00%> (ø)
cmd/gateway_ping.go	0.00% <0.00%> (ø)
cmd/gateway_sync.go	0.00% <0.00%> (ø)
cmd/root.go	0.84% <0.00%> (-0.05%)	⬇️
cmd/gateway_diff.go	0.00% <0.00%> (ø)
cmd/gateway_validate.go	0.00% <0.00%> (ø)
cmd/gateway_reset.go	0.00% <0.00%> (ø)
... and 1 more

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[rspurgeon]

@Tieske @GGabriele This should not be merged. We are not adding the kong at this time. Once we GA the apiops file subcommand we can prioritize the kong command which has deeper repercussions to docs and other guides

[Tieske]

we cannot move the top-level flags now, since that would break the existing commands. That can only be done after we finally remove the compatibility-commands we keep at the top-level.

[GGabriele]

We should fix the tests as part of the d8de662 commit, but other than that LGTM!