Prefix environment variables not read from `.env` files with `OPENVERSE_` to disambiguate them

[sarayourfriend]

Current Situation

Our environment variable practice is slightly error-prone. Variables like SERVICE or DC_USER are sufficiently ambiguous that it wouldn't be surprising if they conflicted with variables set in someone's personal shell environment.

Others, like DISABLE_SENTRY in the frontend, are slightly more "one-off" that it would be surprising if they conflicted and we set those in scripts. It's not unfounded that someone could have DISABLE_SENTRY in their shell environment though, so disambiguating those might not be a bad idea either.

Suggested Improvement

Rename the following environment variables:

• SERVICE -> OPENVERSE_CATALOG_EXEC_SERVICE
• DC_USER -> OPENVERSE_DC_USER
• DISABLE_SENTRY -> OPENVERSE_DISABLE_SENTRY
• TEST_COMMAND -> OPENVERSE_PLAYWRIGHT_TEST_COMMAND

Benefit

Disambiguates these variables. The suggested names above are sometimes more descriptive and self-documenting than the current ones, especially in the monorepo context.

[dhruvkb]

Closely related to https://github.com/WordPress/openverse/issues/1867 (now converted to a tracking issue).