Docs: Create upgrade guide from `v1` to `v2` and deprecation plan for `v1`

[phipag]

What were you searching in the docs?

To allow customers adopt (early versions) of the upcoming Powertools v2 an upgrade guide needs to be created. This will allow us to make alpha releases of v2 and work with early adopters in testing v2 as well as refining the upgrade guide before making a final production release.

Is this related to an existing documentation section?

No response

How can we improve?

Create upgrade guide in v2 documentation and communicate end-of-support / deprecation plan for v1.

Got a suggestion in mind?

Also update v1 documentation to link to v2 documentation in preview mode. Related issue for versioning documentation #1239.

Acknowledgment

• I understand the final update might be different from my proposed suggestion, or refused.

[phipag]

Created version policy page for v1 documentation here: #1823

Next steps:

• Update v2 docs with upgrade guide and version policy
• Update v1 deprecation plan as soon as v2 developer preview starts

[phipag]

PR for upgrade guide #1856