Define maintenance support and add examples on version support

[kawofong]

Temporal Affiliation

• I am a Temporal employee

Content Suggestion

In our versions and support doc, I noted the following enhancements from a customer interaction and an internal thread:

• Maintenance support shall be defined.
• An example of which minor version would be supported vs. not supported when a new minor version is released.

Reference: https://temporaltechnologies.slack.com/archives/C01H1G7J98F/p1749824092025859