docs: fix broken links & link title to VM management

[kelvintaywl]

Description

This PR fixes 2 things around the links to the "Manage virtual machines with (machine provisioner|VM service)" page (example). See Reasons below.

Reasons

• the link to the "Manage virtual machines with (machine provisioner|VM service)" was broken for all v4.x pages.
• the link title says "Managing ..." while the actual page is titled with "Manage ..."

for example, on https://circleci.com/docs/server/v4.1/installation/phase-3-execution-environments/#vm-service, the link to manage VMs points to https://circleci.com/docs/server/v4.1/installation/phase-3-execution-environments/#../operator/manage-virtual-machines-with-vm-service which is invalid.

Content Checklist

Please follow our style when contributing to CircleCI docs. Our style guide is here: https://circleci.com/docs/style/style-guide-overview.

Please take a moment to check through the following items when submitting your PR (this is just a guide so will not be relevant for all PRs) 😸:

• [ ] Break up walls of text by adding paragraph breaks.
• [ ] Consider if the content could benefit from more structure, such as lists or tables, to make it easier to consume.
• [ ] Keep the title between 20 and 70 characters.
• [ ] Consider whether the content would benefit from more subsections (h2-h6 headings) to make it easier to consume.
• [ ] Check all headings h1-h6 are in sentence case (only first letter is capitalized).
• [ ] Is there a "Next steps" section at the end of the page giving the reader a clear path to what to read next?
• [ ] Include relevant backlinks to other CircleCI docs/pages.

[kelvintaywl]

hmm, the lint job is failing but not for the bits I modified 🤔