[core] Prepare libraries for first v7 alpha release

[DiegoAndai]

Important note for reviewers

Reviewing commit per commit will be much easier

Summary

Included in this PR

• Update version tags to next
• Change host to next.mui.com
• Target specific versions of workspace dependencies
• Target next version in examples
• Add v6 to the docs' version dropdown
• Remove some unnecessary #default-branch-switch comments
• Add v7 to the docs' versions table

Not included in this PR

• Any changes to Base or Joy related files

[mui-bot]

Netlify deploy preview

• docs/data/material/components/about-the-lab/about-the-lab.md
• docs/data/material/components/icons/icons.md
• docs/data/material/components/material-icons/material-icons.md
• docs/data/material/getting-started/example-projects/example-projects.md
• docs/data/material/getting-started/installation/installation.md

Bundle size report

No bundle size changes (Toolpad)
No bundle size changes

Generated by 🚫 dangerJS against 3596be6

[DiegoAndai]

We're using #default-branch-switch to mark where changes are required, but with the new protocol, some of these changes happen on master branch and others on v6.x branch, so the comment becomes confusing. There are 4 types of changes that are encompassed under this tag:

• Changes to the npm version tag (latest -> next) in master (This PR)
• Changes to the host (mui.com -> next.mui.com) in master (This PR)
• Changes to repository links (ttps://github.com/mui/material-ui/tree/master -> github.com/mui/material-ui/tree/v6.x) in v6.x (45133)
• Changes to target branches for CI checks/builds (master -> v6.x) in v6.x (45133)

I propose splitting these into 4 different tags:

• #npm-tag-reference
• #host-reference
• #repo-reference
• #target-branch-reference

By splitting them, it will be easier to follow the branch split protocol and understand what each one refers to.

I used reference instead of switch as I think it's more descriptive and reads better: "Here's is a reference of the npm tag/host/repo/target branch"

Let me know if I should go forward with this change @mnajdova.

[mnajdova]

Looks good!