Support "input packages"

[mtojek]

Meta-issue: elastic/package-spec#319

With this PR, elastic-package allows for building the input package, validating it, and exposing it behind the Package Registry. As the Fleet is not ready yet we can see this result:

[2022-06-03T07:01:13.826Z] 2022/06/03 07:01:13 DEBUG POST http://127.0.0.1:5601/api/fleet/epm/packages/sql_input-0.2.0
[2022-06-03T07:01:18.022Z] Installed assets:
[2022-06-03T07:01:18.023Z] Done

In the follow up I will focus on improving field validation, rendering fields table, and importing fields.

[elasticmachine]

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• Start Time: 2022-06-03T07:37:17.405+0000

• Duration: 29 min 2 sec

Test stats 🧪

Test	Results
Failed	0
Passed	720
Skipped	0
Total	720

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (30/30)	💚
Files	64.22% (70/109)	👍
Classes	58.278% (88/151)	👍
Methods	47.421% (285/601)	👍
Lines	32.348% (2616/8087)	👍
Conditionals	100.0% (0/0)	💚

[mtojek]

Hm, based on test errors I deduce that we have to release a new revision of package-spec...

[jsoriano]

Preparing release of the spec elastic/package-spec#329

[mtojek]

/test

[mtojek]

/test