feat(Search): Add support for all Apex language extensions

[mmanela]

Part of GRAPH-759

Linguist only supports a subset of the file extensions often used for the Apex programming languages. This PR adds support for the main set commonly used.

Key changes

1. Adds all extensions for Apex
2. Updates tests

Test plan

• [x] Update unit tests
• [x] Validate zoekt can filter by language
• [x] validate zoekt indexes language appropriately