Re-order update steps in the 8.14 -> 8.15 upgrade guide

Closes #26014

See merge request !8287

Record and show last used date of SSH Keys

See merge request !8113

Fix broken url on group avatar

Closes #26452

See merge request !8464

1. Gems need to be installed before we can run the
  gitlab:workhorse:install task
1. Update gitlab-shell after gitlab-workhorse since it's a manual step
  that needs to be done in `/home/git/gitlab-shell`
Signed-off-by: Rémy Coutable <remy@rymai.me>

Addresses: Issue #13810

1. Adds a last_used_at attribute to the Key table/model
2. Update a key's last_used_at whenever it gets used
3. Display how long ago an ssh key was last used

Fix dead link in Reply by email documentation

Closes #26247

See merge request !8474

Add label to Environments "Date Created" column

Closes #25371

See merge request !8376

Moved the members and groups to single option called members

Closes #25985

See merge request !8281

Re-add Google Cloud Storage as a backup strategy

Closes #26362

See merge request !8481

Improve UX copy docs on capitalization and punctuation

See merge request !8439

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fixed failing markdown button tests

See merge request !8471

Fixed edit form authenticity_token call failing the tests

See merge request !8472

[ci skip]

With Gitea v1.0.0, notes are imported

See merge request !8298

Added animations to issue boards

Closes #25630

See merge request !8417

Fixed padding and margins for the dropdowns on the members section

Precompile all frontend test fixtures

Closes #26226

See merge request !8384

Speed up group milestone index by passing group_id to IssuesFinder

See merge request !8363

Whitelist next project names: assets, profile, public

See merge request !8470

Fix 500 errors when creating a user with identity via API

Closes #26295

See merge request !8442

Changed CSS transition property for only values that change

LDAP attributes needs default values

See merge request !8465

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix timezone due date picker

Closes #24253

See merge request !8081

Replace static JavaScript fixtures for u2f

See merge request !8426

26352 Change Profile settings to User / Settings

Closes #26352

See merge request !8453

Fixed new line being included in bold/italic in GFM form

Closes #25456

See merge request !8086

Resolve "Merge request tabs don't render when no commits available"

Closes #26155 and #24556

See merge request !8347