revisit: add timeout parameter to cli and driver

[avoidik]

this is to revisit unfinished work to bring consistent timeout across all commands:

• improve constant connection timeouts #358
• Allow setting timeout when running docker buildx inspect moby/buildkit#5946
• add timeout parameter to cli and driver #2586
• Consistent timeout parameter #3159

[avoidik]

Same as before:

• --timeout CLI flag
• BUILDX_TIMEOUT environment variable (affects only CLI commands, not driver)
• docker buildx create ... --driver-opt timeout=60s to change it in driver (default timeout is up to a driver's developer)

Defaults: Driver timeout is 120s, the rest is 20s.

[avoidik]

kindly asking for your attention to this PR @tonistiigi

[avoidik]

cc @CamJN please review too