Remove description html text limit

What does this MR do and why?

The description_html text limit was causing problems with forking projects: (internal slack link) https://gitlab.slack.com/archives/CETG54GQ0/p1659983265439899, so we should remove the limit

Closes Unable to fork www-gitlab-com (#370174 - closed)

Migration output

$ bin/rails db:migrate:up:main VERSION=20220808194857
WARNING: This version of GitLab depends on gitlab-shell 14.10.0, but you're running 13.22.0. Please update gitlab-shell.
main: == 20220808194857 RemoveDescriptionHtmlLimit: migrating =======================
main: -- transaction_open?()
main:    -> 0.0000s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("ALTER TABLE namespace_details\nDROP CONSTRAINT IF EXISTS check_2df620eaf6\n")
main:    -> 0.0010s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("ALTER TABLE namespace_details\nDROP CONSTRAINT IF EXISTS check_2f563eec0f\n")
main:    -> 0.0005s
main: == 20220808194857 RemoveDescriptionHtmlLimit: migrated (0.0113s) ==============


main: == 20220808194857 RemoveDescriptionHtmlLimit: migrated (0.0120s) ==============

$ bin/rails db:migrate:down:main VERSION=20220808194857
WARNING: This version of GitLab depends on gitlab-shell 14.10.0, but you're running 13.22.0. Please update gitlab-shell.
main: == 20220808194857 RemoveDescriptionHtmlLimit: reverting =======================
main: -- transaction_open?()
main:    -> 0.0000s
main: -- current_schema()
main:    -> 0.0008s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("ALTER TABLE namespace_details\nADD CONSTRAINT check_2df620eaf6\nCHECK ( char_length(description_html) <= 255 )\nNOT VALID;\n")
main:    -> 0.0008s
main: -- current_schema()
main:    -> 0.0003s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- execute("ALTER TABLE namespace_details VALIDATE CONSTRAINT check_2df620eaf6;")
main:    -> 0.0004s
main: -- execute("RESET statement_timeout")
main:    -> 0.0003s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- current_schema()
main:    -> 0.0002s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("ALTER TABLE namespace_details\nADD CONSTRAINT check_2f563eec0f\nCHECK ( char_length(description) <= 255 )\nNOT VALID;\n")
main:    -> 0.0005s
main: -- current_schema()
main:    -> 0.0002s
main: -- execute("ALTER TABLE namespace_details VALIDATE CONSTRAINT check_2f563eec0f;")
main:    -> 0.0005s
main: == 20220808194857 RemoveDescriptionHtmlLimit: reverted (0.0194s) ==============

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