* [APM] Removes the apm_oss plugin and deprecates related configs (#108160)
* removes commented lines
* fixes typescript errors
* performs start up migration on the saved objects mapping for apm-indices
* removes all references to the deprecated apm_oss.* config paths in APM
* fixes missing bundle error
* fixes type error
* fixes eslint error with disabled rules
* fixes saved object mappings for es_archvices for tests
* fixes eslint error
* Updates default index values to include the more general apm-*. Fixes broken tests.
* removing unused configs from the config path migration: apm_oss.indexPattern and apm_oss.fleetMode
* - replaces full index configuration paths with references in the `xpack.apm.indices` namespace
- removes mergeConfig function and test
* fixes proxy mock object in unit test
* fixes linting issues
* PR feedback and failed test
* changes the configs at `xpack.apm.indices.*` from plural to singular to match `processor.event` values
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