[IngestManager] Move RequiredPackage type near DefaultPackages

[jfsiii]

Summary

• Move the RequiredPackage type to the same location as DefaultPackages so anyone looking at one will see the other as well
• New approach to defining & using enum-like values.

The basic outline of the approach

1. Export a JS object as const from common/constants/* (expose runtime value)
   

   kibana/x-pack/plugins/ingest_manager/common/constants/epm.ts

   Lines 12 to 15 in d66cf60

   	export const requiredPackages = {
   	System: 'system',
   	Endpoint: 'endpoint',
   	} as const;

2. Import that JS value and convert to a TS type as type TSType = typeof jsValue
   
3. The values (right-hand side) of that type can be converted to a union type with ValueOf<X>
   
4. The values can be accessed as TS types TSType['key'] or JS jsValue.key

This way we

• still get the readability of TS enums
• can choose to only import the types of values we need (compile time or runtime)
• use the TS utility types like Pick, Omit, etc

More detail on 1

• Value which can be access/iterated at runtime, e.g. Object.values(requiredPackages) or requiredPackages.System
• narrows the type those exact values, not string
  
• can't be modified (it's readonly)
  

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[jfsiii]

@elasticmachine merge upstream

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: d66cf60

Metrics [docs]

page load bundle size

id	before	after	diff
ingestManager	385.5KB	385.8KB	+293.0B

History

• 💚 Build #84945 succeeded fba2982

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[jfsiii]

@nchaulet I changed the specific implementation here (object vs array) but merging b/c it's similar to what's approved and will be consistent with forthcoming PR's to replace enums and ValueOf type will be used in those.

[kibanamachine]

Looks like this PR has a backport PR but it still hasn't been merged. Please merge it ASAP to keep the branches relatively in sync.