Refactor packages: rename REST tracker API packages

[josecelano]

Hi @da2ce7 , I'm considering renaming packages related to the REST Tracker API:

Dir:

• axum-tracker-api-server -> axum-rest-tracker-api-server
• tracker-api-core -> rest-tracker-api-core
• tracker-api-client -> rest-tracker-api-client

Crates:

• torrust-axum-tracker-api-server -> torrust-axum-rest-tracker-api-server
• torrust-tracker-api-core -> torrust-rest-tracker-api-core
• torrust-tracker-api-client -> torrust-rest-tracker-api-client

Mod name:

• torrust_axum_tracker_api_server -> torrust_axum_rest_tracker_api_server
• torrust_tracker_api_core -> torrust-rest_tracker_api_core
• torrust_tracker_api_client -> torrust_rest_tracker_api_client

Since we have started considering adding a GraphQL API and the those crates are not published yet, we will avoid ambiguity in the future. We could name the new packages:

• axum-graphql-tracker-api-server (torrust-axum-graphql-tracker-api-server)
• graphql-tracker-api-core(torrust-graphql-tracker-api-core)