Show error if assets are being exported using a Elastic stack SNAPSHOT version

[mrodm]

Closes elastic/package-spec#318

This PR shows an error when assets are exported from an Elastic stack SNAPSHOT version. Using those assets generated by a snapshot version may lead to use features that are not released at the end, or maybe they are in a different way.

In case developers need to use an SNAPSHOT version, a new parameter has been added --allow-snapshots to allow this export process.

Output using SNAPSHOT Version:

• Running elastic-package export dashboards:

   $ elastic-package export dashboards 
  elastic-package has been installed.
  Export Kibana dashboards
  Error: exporting dashboards from a SNAPSHOT version of Kibana (8.4.0-SNAPSHOT) is discouraged. It could lead to invalid dashboards (for example if they use features that are reverted or modified before the final release). --allow-snapshot flag can be used to ignore this error
  

• Running elastic-package export dashboards --allow-snapshot:

   $ elastic-package export dashboards --allow-snapshot
  Export Kibana dashboards
  Warning: exporting dashboards from a SNAPSHOT version of Kibana (8.4.0-SNAPSHOT) is discouraged. It could lead to invalid dashboards (for example if they use features that are reverted or modified before the final release)
  ? Which dashboards would you like to export?  [Use arrows to move, space to select, <right> 
  to all, <left> to none, type to filter]
  ...
  

Tested with 8.0.0, 8.4.0-SNAPSHOT and 7.17.6 and 7.17.0-SNAPSHOT versions.

In this PR, the /api/status endpoint is being tested to retrieve the version information. This includes a dedicated field about whether or not this is a snapshot build (build_snapshot field).

• Running command elastic-package stack up -v -d --version 8.0.0:

 $ curl -u elastic:changeme -H 'Content-Type: application/json' -H 'kbn-xsrf: true' -k -s https://localhost:5601/api/status? | jq -r .version
{
  "number": "8.0.0",
  "build_hash": "57ca5e139a33dd2eed927ce98d8231a1f217cd15",
  "build_number": 49192,
  "build_snapshot": false
}

• Running command elastic-package stack up -v -d --version 8.4.0-SNAPSHOT:

 $ curl -u elastic:changeme -H 'Content-Type: application/json' -H 'kbn-xsrf: true' -k -s https://localhost:5601/api/status | jq -r .version
{
  "number": "8.4.0",
  "build_hash": "7ffc375be69ab56267d3fc71bf7f27da6dfacdfb",
  "build_number": 55408,
  "build_snapshot": true
}

In case of build_snapshot true , it must be added the suffix "-SNAPSHOT" to the version.number field.

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• Start Time: 2022-09-21T15:13:28.636+0000

• Duration: 37 min 54 sec

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Name	Metrics % (covered/total)	Diff
Packages	100.0% (34/34)	💚
Files	66.142% (84/127)	👎 -0.787
Classes	61.111% (110/180)	👎 -0.556
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[jsoriano]

👍 some nitpicking in the error messages.

[mrodm]

Version method from internal/kibana/injected_metadata.go deleted in favor of this one.

This new method uses the /api/status endpoint, and it has a dedicated field to indicate whether or not the version is a snapshot one (build_snapshot).

[jsoriano]

Wdyt about returning an object with the version information instead of multiple values?

Suggested change

	func (c *Client) Version() (string, bool, error) {
	func (c *Client) Version() (VersionInfo, error) {

[mrodm]

Sure! Added that new object.

[mrodm]

This API returns the version without -SNAPSHOT. https://github.com/elastic/kibana/blob/main/packages/core/status/core-status-server-internal/src/routes/status.ts#L120-L123

That's why it is needed to be added here.

Example of output (Elastic stack 7.17.0-SNAPSHOT):

 $ curl -u elastic:changeme -H 'Content-Type: application/json' -H 'kbn-xsrf: true' -k -s https://localhost:5601/api/status | jq -r .version
{
  "number": "7.17.0",
  "build_hash": "0ab325e4b36168a264907fbc84f6913519671acf",
  "build_number": 46537,
  "build_snapshot": true
}