Extend database with encrypted field for static objects tokens

What does this MR do and why?

Contributes to #199716 (closed)

Roadmap

1. Add database fields for encrypted tokens <- This MR
2. Migrate old tokens to encrypted version and start using them
3. Drop plaintext token fields (TODO)

Problem

We store "static_objects_external_storage_auth_token" in plaintext. This is the first step, where we define a new database field where encrypted value will be stored.

Solution

Add a database field to store an encoded version of the token

Database

Migration

== 20211124132319 AddEncryptedStaticObjectsExternalStorageAuthToken: migrating
-- add_column(:application_settings, :static_objects_external_storage_auth_token_encrypted, :text)
   -> 0.0035s
== 20211124132319 AddEncryptedStaticObjectsExternalStorageAuthToken: migrated (0.0035s)

== 20211126113029 AddTextLimitForStaticObjectsExternalStorageAuthToken: migrating
-- transaction_open?()
   -> 0.0000s
-- current_schema()
   -> 0.0002s
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE application_settings\nADD CONSTRAINT check_32710817e9\nCHECK ( char_length(static_objects_external_storage_auth_token_encrypted) <= 255 )\nNOT VALID;\n")
   -> 0.0035s
-- current_schema()
   -> 0.0002s
-- execute("SET statement_timeout TO 0")
   -> 0.0006s
-- execute("ALTER TABLE application_settings VALIDATE CONSTRAINT check_32710817e9;")
   -> 0.0014s
-- execute("RESET statement_timeout")
   -> 0.0007s
== 20211126113029 AddTextLimitForStaticObjectsExternalStorageAuthToken: migrated (0.0210s)

Rollback

== 20211126113029 AddTextLimitForStaticObjectsExternalStorageAuthToken: reverting
-- transaction_open?()
   -> 0.0000s
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE application_settings\nDROP CONSTRAINT IF EXISTS check_32710817e9\n")
   -> 0.0018s
== 20211126113029 AddTextLimitForStaticObjectsExternalStorageAuthToken: reverted (0.0129s)

== 20211124132319 AddEncryptedStaticObjectsExternalStorageAuthToken: reverting
-- remove_column(:application_settings, :static_objects_external_storage_auth_token_encrypted)
   -> 0.0054s
== 20211124132319 AddEncryptedStaticObjectsExternalStorageAuthToken: reverted (0.0055s)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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