Remove association between ChatName and Integration - Step 2

What does this MR do and why?

Per issue, the MR introduces:

• updates the ChatNames::AuthorizeUserService to not take an integration (the #chat_name_params in that class will have no integration_id)
• updates the Gitlab::ChatNameToken#get to not retrieve integration_id
• removes CONSTRAINT CHECK (introduced an irreversible migration)
• removes presence validation

In addition, it solves the #370308 (closed)

Database Migration

• Output of db:migrate

$ scripts/db_tasks db:migrate
main: == 20221228083452 RemoveCheckConstraintOnChatNamesOnIntegration: migrating ====
main: -- transaction_open?()
main:    -> 0.0000s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("            ALTER TABLE chat_names\n            DROP CONSTRAINT IF EXISTS check_2b0a0d0f0f\n")
main:    -> 0.0015s
main: == 20221228083452 RemoveCheckConstraintOnChatNamesOnIntegration: migrated (0.0150s) 

• Output of db:rollback

$ scripts/db_tasks db:migrate:down VERSION=20221228083452
main: == 20221228083452 RemoveCheckConstraintOnChatNamesOnIntegration: reverting ====
main: -- transaction_open?()
main:    -> 0.0000s
main: -- current_schema()
main:    -> 0.0007s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("ALTER TABLE chat_names\nADD CONSTRAINT check_2b0a0d0f0f\nCHECK ( integration_id IS NOT NULL )\nNOT VALID;\n")
main:    -> 0.0011s
main: -- current_schema()
main:    -> 0.0004s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0004s
main: -- execute("ALTER TABLE chat_names VALIDATE CONSTRAINT check_2b0a0d0f0f;")
main:    -> 0.0007s
main: -- execute("RESET statement_timeout")
main:    -> 0.0004s
main: == 20221228083452 RemoveCheckConstraintOnChatNamesOnIntegration: reverted (0.0258s) 

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #384973 (closed)