Move support branches docs to team docs

[36degrees]

The process for using a support branch is being moved into our team docs as part of alphagov/design-system-team-docs#21.

Remove the existing documentation and add a reference to it in our standard docs on publishing releases.

[colinrotherham]

Will we leave the v4 docs in place on support/4.x?

Aware we still have this PR to discuss/backport to bring them back in line:

• [support/4.x] Backport: Publishing docs changes, versioning #4001

[dav-idc]

Hi @36degrees we noticed in the Design System standup today that this issue is in need of review and is labelled as cross-squad. Would it be ready for review?

[36degrees]

Will we leave the v4 docs in place on support/4.x?

I've raised additional PRs for support/4.x (#4234) and support/3.x (#4235)

[github-actions]

📋 Stats

File sizes

File	Size
dist/govuk-frontend-4.6.0.min.css	118.07 KiB
dist/govuk-frontend-4.6.0.min.js	47.1 KiB
dist/govuk-frontend-ie8-4.6.0.min.css	79.27 KiB
packages/govuk-frontend/dist/govuk/all.bundle.js	75.84 KiB
packages/govuk-frontend/dist/govuk/all.bundle.mjs	71.24 KiB
packages/govuk-frontend/dist/govuk/all.mjs	3.84 KiB
packages/govuk-frontend/dist/govuk/govuk-frontend-component.mjs	359 B
packages/govuk-frontend/dist/govuk/govuk-frontend.min.js	36.79 KiB
packages/govuk-frontend/dist/govuk/i18n.mjs	5.83 KiB

Modules

File	Size
all.mjs	67.34 KiB
components/accordion/accordion.mjs	21.9 KiB
components/button/button.mjs	4.71 KiB
components/character-count/character-count.mjs	21.64 KiB
components/checkboxes/checkboxes.mjs	5.41 KiB
components/error-summary/error-summary.mjs	6.01 KiB
components/exit-this-page/exit-this-page.mjs	16.6 KiB
components/header/header.mjs	3.34 KiB
components/notification-banner/notification-banner.mjs	4.54 KiB
components/radios/radios.mjs	4.41 KiB
components/skip-link/skip-link.mjs	3.73 KiB
components/tabs/tabs.mjs	9.07 KiB

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