Verify LFS OID

What does this MR do and why?

Currently the oid on our LfsObjects aren't verified for their format. This MR introduces a regex check for /\A\h{64}\z/ to ensure the oids are well-formed.

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How to set up and validate locally

In the rails console for an invalid oid:

[1] pry(main)> LfsObject.create!(oid: "notvalid",size: 1234,file: nil)
Creating scope :verification_succeeded. Overwriting existing method LfsObject.verification_succeeded.
Creating scope :verification_failed. Overwriting existing method LfsObject.verification_failed.
Creating scope :checksummed. Overwriting existing method LfsObject.checksummed.
Creating scope :not_checksummed. Overwriting existing method LfsObject.not_checksummed.
Creating scope :available_verifiables. Overwriting existing method LfsObject.available_verifiables.
  TRANSACTION (0.1ms)  BEGIN /*application:console,db_config_name:main,line:(pry):1:in `__pry__'*/
  LfsObject Exists? (2.3ms)  SELECT 1 AS one FROM "lfs_objects" WHERE "lfs_objects"."oid" = 'notvalid' LIMIT 1 /*application:console,db_config_name:main,line:(pry):1:in `__pry__'*/
  TRANSACTION (0.1ms)  ROLLBACK /*application:console,db_config_name:main,line:/lib/gitlab/database.rb:370:in `rollback'*/
ActiveRecord::RecordInvalid: Validation failed: Oid is invalid
from /home/joern/.asdf/installs/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/activerecord-6.1.6.1/lib/active_record/validations.rb:80:in `raise_validation_error'
[2] pry(main)> 

For a valid oid:

[2] pry(main)> LfsObject.create!(oid: "a"*64,size: 1234,file: nil)
  TRANSACTION (0.3ms)  BEGIN /*application:console,db_config_name:main,line:(pry):2:in `__pry__'*/
  LfsObject Exists? (0.4ms)  SELECT 1 AS one FROM "lfs_objects" WHERE "lfs_objects"."oid" = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' LIMIT 1 /*application:console,db_config_name:main,line:(pry):2:in `__pry__'*/
  LfsObject Create (67.5ms)  INSERT INTO "lfs_objects" ("oid", "size", "created_at", "updated_at", "file") VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 1234, '2022-08-01 15:01:36.087915', '2022-08-01 15:01:36.087915', 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa') RETURNING "id" /*application:console,db_config_name:main,line:(pry):2:in `__pry__'*/
  LfsObject Update (1.3ms)  UPDATE "lfs_objects" SET "file_store" = 1 WHERE "lfs_objects"."id" = 19 /*application:console,db_config_name:main,line:/app/models/concerns/file_store_mounter.rb:24:in `update_file_store'*/
  LfsObject Exists? (0.3ms)  SELECT 1 AS one FROM "lfs_objects" WHERE "lfs_objects"."file_store" = 1 AND "lfs_objects"."id" = 19 LIMIT 1 /*application:console,db_config_name:main,line:/ee/app/models/concerns/geo/verifiable_model.rb:19:in `save_verification_details'*/
  Geo::LfsObjectState Load (10.7ms)  SELECT "lfs_object_states".* FROM "lfs_object_states" WHERE "lfs_object_states"."lfs_object_id" = 19 LIMIT 1 /*application:console,db_config_name:main,line:/ee/app/models/ee/lfs_object.rb:64:in `lfs_object_state'*/
  Geo::LfsObjectState Create (0.5ms)  INSERT INTO "lfs_object_states" ("lfs_object_id") VALUES (19) RETURNING "lfs_object_id" /*application:console,db_config_name:main,line:/ee/app/models/concerns/geo/verifiable_model.rb:28:in `save_verification_details'*/
  TRANSACTION (0.2ms)  COMMIT /*application:console,db_config_name:main,line:/lib/gitlab/database.rb:364:in `commit'*/
  GeoNode Exists? (0.4ms)  SELECT 1 AS one FROM "geo_nodes" LIMIT 1 /*application:console,db_config_name:main,line:/ee/lib/gitlab/geo.rb:86:in `block in enabled?'*/
=> #<LfsObject:0x000055eedd55d058
 id: 19,
 oid: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
 size: 1234,
 created_at: Mon, 01 Aug 2022 15:01:36.087915577 UTC +00:00,
 updated_at: Mon, 01 Aug 2022 15:01:36.087915577 UTC +00:00,
 file: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
 file_store: 1,
 verification_checksum: nil>

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