Merge meta.yaml and che-plugin.yaml

[garagatyi]

What does this PR do?

This PR reworks plugin broker to process meta.yaml with new structure.
Complete change of components needed to create this PR is described here eclipse-che/che#12908 (comment)
Plugins with new meta are placed in v3 folder of Che plugin registry https://github.com/eclipse/che-plugin-registry/tree/master/v3/plugins
What is changed in details:

• configuration that was earlier part of che-plugin.yaml now is part of meta.yaml. In particular che-plugin-yaml content is placed in spec field of meta.yaml
• meta.yaml now contains apiVersion field. This PR requires meta.yaml to contain apiVersion: v2 since current version of meta yaml is considered v1. This field will allow us to implement backward compatibility for future changes of meta.yaml model
• setting fields url, extension, extensions, attributes in meta.yaml is no longer supported
• both VS code extension and Theia plugin have to specify URLs to binaries archives/IDs of vscode extensions in spec.extensions field, which is array.
• VS code extension broker and Theia plugin brokers are merged into a single one to cleanup the code. Which leads to a new feature - both VS code extension and Theia plugin can specify both .theia and vsix archives in it and they are properly processed. This makes both types of extensions effectively the same.
• Specifying sidecar image in package.json of .theia plugin is no longer supported
• Usage of tar archives for plugins of types Che plugin, Che editor is no longer supported.
• Plugins of all types (including VS Code and Theia) can specify the same sidecar configuration such as RAM limit, environment variables, volumes, ports, etc.
• Field with commands that was called editorCommands in che-plugin.yaml renamed in commands in meta.yaml
• Copying files from Che editor/Che plugin tar archives is no longer supported
• Setting of editors field from che-plugin.yaml is no longer supported
• New feature: Theia plugin now supports specifying several archives
• Che plugin broker is removed since it is no longer needed.

Current limitations:

• VS Code extension/Theia plugin can have only 1 sidecar and can not specify endpoint for the time being

Examples of metas (more details at eclipse-che/che#12908 (comment)):

• VS code extension with several archives and sidecar image specified https://gist.githubusercontent.com/garagatyi/0ae0f6a05b76e504c9152e6eef160917/raw/plugin-vscode.yaml. To make it local to Theia container remove containers field. The same content can be used as a plugin of type Theia plugin if type is replaced accordingly.
• Example of the same extension when RAM limit is specified https://gist.githubusercontent.com/garagatyi/0ae0f6a05b76e504c9152e6eef160917/raw/plugin-vscode-with-ram.yaml
• Not supported yet example (see limitation note above) with other fields https://gist.githubusercontent.com/garagatyi/0ae0f6a05b76e504c9152e6eef160917/raw/plugin-vscode-extended.yaml.

What issues does this PR fix or reference?

Related to eclipse-che/che#12908

[garagatyi]

Code is ready, there is still a test file to fix left. I'm working on fixing it ATM

[garagatyi]

@svor I'm adding feature of using both .theia and .vsix in the same Che plugin. I suppose it is something you need.
@tsmaeder Please, read the description of the change. This can be valuable for languages team planning of features delivery.

[codecov]

Codecov Report

Merging #55 into master will increase coverage by 0.95%.
The diff coverage is 91.83%.

@@            Coverage Diff             @@
##           master      #55      +/-   ##
==========================================
+ Coverage   61.43%   62.38%   +0.95%     
==========================================
  Files           8        6       -2     
  Lines         809      553     -256     
==========================================
- Hits          497      345     -152     
+ Misses        264      182      -82     
+ Partials       48       26      -22

Impacted Files	Coverage Δ
storage/storage.go	100% <100%> (+11.11%)	⬆️
brokers/unified/vscode/sidecar.go	100% <100%> (ø)
brokers/unified/vscode/broker.go	74.51% <87.27%> (ø)
brokers/unified/broker.go	80.51% <90.9%> (+9.31%)	⬆️

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[amisevsk]

LGTM, with a few comments.