[TASK] Reduce usage to tx_ter_extensions

This patch changes
- the extensions.xml generator
- various logic regarding checks if a version exists
to not query the tx_ter_extensions database table anymore.

Now the only place where tx_ter_extensions is actually used
is the SOAP API Upload and the Migration to tx_terfe2_* db structure
which will be migrated in the next patch.
7 jobs for feature/reduce_usages_to_terv1_db in 3 minutes and 23 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Maintenance
manual Get dump for local environment #21639
allowed to fail manual
 
  Test
passed test:composer #21642

00:02:06

passed test:php #21641

00:01:46

passed test:typoscript #21640

00:02:16

failed test:unit #21643

00:03:21

 
  Build
skipped build #21644
 
  Layout
skipped layout #21645
 
Name Stage Failure
failed
test:unit Test
     </version>\n

/builds/t3o/ter/extensions/ter_fe2/Tests/Unit/Service/ExtensionIndexServiceTest.php:100
/builds/t3o/ter/vendor/phpunit/phpunit/phpunit:61

FAILURES!
Tests: 50, Assertions: 65, Failures: 1.
Script ./vendor/bin/phpunit -c .gitlab-ci/Tests/UnitTests.xml handling the test:unit event returned with error code 1
ERROR: Job failed: exit code 1