pandaproxy/sr: Improve schema lookup

[IoannisRP]

Change lookup strategy to always apply active transformation to existing schemas, instead of only applying it when normalisation is turned on.

Motivation:

This allows a specific workflow performed by SR clients following this pattern to lookup schema IDs:

• POST /subject/sub/versions?normalize=true -d {schema}
• GET /subject/sub/versions/latest -> this returns the schema and latest version but NOT IDs
• POST /subject/sub -d {schema-from-get} -> this returns ID

In our SR, a call to POST /subject/sub without normalize=true will result in this schema being sanitized which may change the content of the schema. With this change, both input schema and lookup schema go through the same operation and still be deemed equal.

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v24.3.x
• v24.2.x
• v24.1.x

Release Notes

• none

[vbotbuildovich]

CI test results

test results on build#61843

test_id	test_kind	job_url	test_status	passed
rptest.tests.compaction_recovery_test.CompactionRecoveryTest.test_index_recovery	ducktape	https://buildkite.com/redpanda/redpanda/builds/61843#01950084-c44a-4035-a07a-1f9b982d678c	FLAKY	1/2
rptest.tests.compaction_recovery_test.CompactionRecoveryTest.test_index_recovery	ducktape	https://buildkite.com/redpanda/redpanda/builds/61843#019500a1-0b2c-46b3-8096-8bf14f420977	FLAKY	1/2
rptest.tests.log_compaction_test.LogCompactionTest.compaction_stress_test.cleanup_policy=compact.key_set_cardinality=1000.storage_compaction_key_map_memory_kb=10	ducktape	https://buildkite.com/redpanda/redpanda/builds/61843#019500a1-0b2b-453d-8433-deb9178592fe	FLAKY	1/2
rptest.tests.scaling_up_test.ScalingUpTest.test_scaling_up_with_recovered_topic	ducktape	https://buildkite.com/redpanda/redpanda/builds/61843#019500a1-0b2c-46b3-8096-8bf14f420977	FLAKY	1/2

[vbotbuildovich]

/backport v24.3.x

[vbotbuildovich]

/backport v24.2.x