Update the documentation to reflect the changes made for the next
FuseML release. Also includes fixing some typos and formating.

(cherry picked from commit 77d10be)

[0.3] Update docs for release v0.3

[0.3] Build and switch latest docs to v0.3

(cherry picked from commit d0798c0)

[0.3] Update OpenAPI specification with latest API

[0.3] Update repository references to point to 0.3 branch

(cherry picked from commit 0d21b45)

This documentation section is based on the Extension Registry
blueprint published in the fuseml/fuseml repository [1], with some
minor changes to make it more suitable for end users and to provide
more up-to-date and relevant examples.

[1] https://github.com/fuseml/fuseml/blob/main/docs/blueprints/003-extension-registry.md

(cherry picked from commit 1feb029)

This documentation section is based on the Installer Extensions
blueprint published in the fuseml/fuseml repository [1], with some
minor changes to make it more suitable for end users and to provide
more up-to-date and relevant examples.

[1] https://github.com/fuseml/fuseml/blob/main/docs/blueprints/001-installation-of-extensions.md

(cherry picked from commit 80160d5)

[0.3] Document workflows and extensions

(cherry picked from commit be27f8c)

[0.3] Document kserve, seldon-core and ovms workflow extensions