DLPX-84378 Update docs package dependencies to latest version in virtualization-sdk

[SumoSourabh]

Background

We are using a very old version of mkdocs and mkdocs-material. Also, there are 4 open PR to update the dependencies.

Problem

As we are using a very old versions of mkdocs and mkdocs-material, which has certain security risks.

Evaluation

The security concerns are caused due to old version of mkdocs.

Solution

1. Update mkdocs 0.17.5 -> 1.4.2
2. Update mkdocs-material 2.9.2 -> 9.0.6
3. Update python from 3.7 -> 3.8
4. Update absolute links to relative links as mkdpcs version > 1.0.0 does not support absolute links.
5. Made some changes to UI look to incorporate some new features.

Important

1. Please refer https://github.com/delphix/docs-masking on the reason to delete the fullmaterial folder. As the overrides are no more required to remove certain header and customising the CSS.
2. Added delphix-brand.css which helps in keeping the color, logo size, admonition and tables as per the previous formats.
3. PR that will be closed
   • Bump mkdocs from 0.17.5 to 1.2.3 in /docs by dependabot[bot] · Pull Request #406 · delphix/virtualization-sdk
   • Bump pygments from 2.6.1 to 2.7.4 in /docs by dependabot[bot] · Pull Request #363 · delphix/virtualization-sdk
   • Bump pyyaml from 5.3.1 to 5.4 in /docs by dependabot[bot] · Pull Request #361 · delphix/virtualization-sdk
   • Bump jinja2 from 2.11.2 to 2.11.3 in /docs by dependabot[bot] · Pull Request #359 · delphix/virtualization-sdk
4. Also, merging the PR will remove 6 security concerns https://github.com/delphix/virtualization-sdk/security/dependabot for the repo.

Testing done

• Compared developer.delphix.com and Changes dveloper.delphix.com for similarties.
• Used linkcheck to confirm all links are working fine.
• All checked the changes on mobile.

Bonus

• Updated the python version to 3.8
• Removed all unused / redundant files (full material folder)
• Added support for linkcheck.

[ravi-cm]

And all the files removed are no longer required?

Ship-it once comments are resolved.