Removed custom DB overrides in favour of in-container variables.

[AlexSkrypnyk]

there were 3 levels of DB-ralted variables:

1. DREVOPS_MARIADB_*
2. MARIADB_*
3. defaults

The purpose of DREVOPS_MARIADB_* was to allow platform-independent DB credentials. But in practice, those are never changed in projects.

In addition, having these values only in .env and not directly in docker-compose.yml does not allow to run docker compose exec * commands with those variables loaded. As a result, docker compose exec drush st cannot connect to the local DB.

Note that DREVOPS_MARIADB_* was used only locally. MARIADB_* is injected by Lagoon. For other providers, these are added through whole $database variable override (like Acquia), so these are not used in prod at all.

[codecov]

Codecov Report

Merging #1017 (db1a0d8) into develop (c4d329d) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##           develop    #1017   +/-   ##
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  Coverage    71.90%   71.90%           
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  Files           50       50           
  Lines         3509     3509           
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  Hits          2523     2523           
  Misses         986      986           

Files	Coverage Δ
scripts/drevops/info.sh	0.00% <0.00%> (ø)