[Extension] Rename `upgrade` to `update`

[hemarina]

Scenario

We currently have a blend of update and upgrade and we want to have consistency.

• azd update - update to the latest version of azd
• azd ext upgrade - update extension to latest version of that extension

Change

• change extension upgrade to update for consistency across the CLI
• change hints to update
• keep azd ext upgrade as an alias (so we don't have a breaking change)

Original post on this issue:
Related to: #7002 (comment)
I prefer to rename extension upgrade to update for consistency of core azd and for industry standard usage. Open to discussion if we want to update this.

[kristenwomack]

Yes, I fully support this Marina He (@hemarina)

[JeffreyCA]

Same, though I'd prefer we keep azd ext upgrade as an alias to not disrupt existing users. I don't think we need to display a deprecated warning either.

[JeffreyCA]

I think this also applies to azd tool upgrade

[hyoshis]

Changing all the commands and customer facing text from upgrade to update for consistency and meeting the industry standards.