refactor(stages): Fixed alias matching, added fallback and unit tests

[alanmquach]

Experimental: This would allow multiple implementations of a single stage type. Similar to how a specific type can be provided by multiple cloud providers, but in this case we use a generic altKey instead of cloudProvider for matching.

[anotherchrisberry]

Does this buy us anything over using alias?

[alanmquach]

I was thinking this would have absolutely 0 dependency on anything in orca, but let me take a look and play with alias a bit more.

[alanmquach]

Turns out alias almost works like a charm.

I ended up only having to refactor PipelineRegistry.getStageConfig() a bit to fix the corner case where aliasing to an existing key would break the existing stage. For example, simply registering a new { key: 'foo', alias: 'wait' } stage would break wait because:

• getStageConfig returns null
• this is because the existence of an extra alias increases the number of matches (since the existing filter included stageType.alias === stage.type)
• this ends up bumping typical things from 1 match to 2 (or more), causing it to go into the default block of the switch statement (which only handles finding a cloudProvider specific stage type)
• stages that don't have cloud providers would simply return null

This is basically what the new unit test matches redirect targets to ensure the actual stages do not get broken simply by having other stages alias to them will now protect against.

Finally, also added the ability to gracefully degrade back to the aliased stage (wait in the above example) if aliasing stage (foo) is ever deleted/deprecated from deck.

[anotherchrisberry]

nice