Increase text limit of maintainer_note field

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR increases the text limit associated with the ci_runners' maintainer_note field from 255 to 1024, in order to provide more room for runner maintainers to keep their notes.

Screenshots or screen recordings

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How to set up and validate locally

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

Migration

bin/rails db:migrate

$ bin/rails db:migrate
lg
== 20220221102333 ChangeMaintainerNoteLimitInCiRunner: migrating ==============
-- transaction_open?()
   -> 0.0000s
-- current_schema()
   -> 0.0003s
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE ci_runners\nADD CONSTRAINT check_ce275cee06\nCHECK ( char_length(maintainer_note) <= 1024 )\nNOT VALID;\n")
   -> 0.0017s
-- current_schema()
   -> 0.0002s
-- execute("SET statement_timeout TO 0")
   -> 0.0005s
-- execute("ALTER TABLE ci_runners VALIDATE CONSTRAINT check_ce275cee06;")
   -> 0.0009s
-- execute("RESET statement_timeout")
   -> 0.0006s
-- transaction_open?()
   -> 0.0000s
-- transaction_open?()
   -> 0.0000s
-- execute("ALTER TABLE ci_runners\nDROP CONSTRAINT IF EXISTS check_56f5ea8804\n")
   -> 0.0009s
== 20220221102333 ChangeMaintainerNoteLimitInCiRunner: migrated (0.0216s) =====

bin/rails db:rollback

$ bin/rails db:rollback RAILS_ENV=development
== 20220221102333 ChangeMaintainerNoteLimitInCiRunner: reverting ==============
== 20220221102333 ChangeMaintainerNoteLimitInCiRunner: reverted (0.0000s) =====

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.

Part of #348299 (closed)