feat: add --set-json flag to set json values.

[lucadirocco]

When used with helm install, helm template, helm upgrade, it enables
to set json values (scalars/objects/arrays) from the command line.

Closes #10428

Signed-off-by: Luca Di Rocco lucadirocco@gmail.com

What this PR does / why we need it:
This PR allows to set any key of the exposed values (scalars, objects, arrays) of a chart, by using a json value on the command line.
It become easier and more concise to update entire portions of the exposed values, as json data structures on command line, rather than setting the value of each individual leaf attribute of the data structure (#10428 provides an example)

Special notes for your reviewer:
The implementation has tried to reuse as much as possible the existing code and the standard libraries, and is quite straightforward.
There are some obvious changes in cmd/helm/flags.go and pkg/cli/values/options.go in order to include the new option flag (--set-json)
The parser logic from pkg/strvals/parser.go is reused, with an extra field in the parser struct (isjsonval bool, true only for --set-json) and some extra code in the following two functions, to parse a json value when a "=" char is met:
func (t *parser) key(data map[string]interface{}) (reterr error)
func (t *parser) listItem(list []interface{}, i int) ([]interface{}, error)

If applicable:

• this PR contains documentation
  Little updates in the description constants of cmd/helm/install.go and cmd/helm/upgrade.go to.
  Together with the info from cmd/helm/flags.go, this should update the documentation when "helm docs --type markdown --generate-headers" is executed.
• this PR contains unit tests
  Some extra unit tests with function TestParseJSON in pkg/strvals/parser_test.go
• this PR has been tested for backwards compatibility
  All unit test run, I don't know if something else is required. Being this a new feature, there are no changes in existing functionalities.
  Please note that I had also to remove the ending new line '\n' from an errors.Errorf statement in the
  func compare(actual []byte, filename string) error, in file ./internal/test/test.go, because go lint was failing and also tests were not running.

[joejulian]

What happens if the flag is specified twice with conflicting values or subsets of values?

--set-json='foo={"key1":"value1","key2":"value2"}' --set-json='foo.key2="bar"'

or

--set-json='foo=["one", "two", "three"]' --set-json='foo=["four"]'

[lucadirocco]

Similarly to the other --set-x flags, for each key the rightmost assignment prevails.
This implies that with --set-json='foo={"key1":"value1","key2":"value2"}' --set-json='foo.key2="bar"' foo is set to {"key1":"value1","key2":"bar"}
while with --set-json='foo=["one", "two", "three"]' --set-json='foo=["four"]' foo is set to ["four"]

[joejulian]

Should this be explicitly called out in documentation?

[lucadirocco]

Sure. I can add some more info/examples to install.go and upgrade.go.

[lucadirocco]

@joejulian
I have checked that in cmd/helm/install.go (const installDesc) it is already explained the behavior of the --set flag when it is specified multiple times.
I have added the above examples in order to highlight a similar behavior with --set-json:

You can specify the ‘–set’ flag multiple times. The priority will be given to the last (right-most) set specified. For example, if both ‘bar’ and ‘newbar’ values are set for a key called ‘foo’, the ‘newbar’ value would take precedence:

$ helm install --set foo=bar --set foo=newbar  myredis ./redis

Similarly, in the following example ‘foo’ is set to ‘[“four”]’:

$ helm install --set-json='foo=["one", "two", "three"]' --set-json='foo=["four"]' myredis ./redis

And in the following example, ‘foo’ is set to ‘{“key1”:“value1”,“key2”:“bar”}’:

$ helm install --set-json='foo={"key1":"value1","key2":"value2"}' --set-json='foo.key2="bar"' myredis ./redis

[joejulian]

LGTM, but I'm not an approver.

[hickeyma]

LGTM, thanks @lucadirocco

[lucadirocco]

LGTM, thanks @lucadirocco

Thank you @hickeyma

[hickeyma]

This need approval from another maintainer to merge.

[sabre1041]

LGTM