registry tool plugins, enforcing lower-case restrictions on resource names

• Following AIP-122, we require that resource names be lowercase.
• Assorted improvements were made to the registry tool's linter plugin
• A new kubectl-style plugin mechanism was added that, for example, allows registry-experimental subcommands to be called from the registry tool with registry experimental.

Changelog

• 2023f33 show available plugins in registry cli (#1167)
• ce5d8c3 remove glob chars from spectral target filename (#1165)
• b04c507 add debug flag that retains temporary files (#1166)
• 2d8c94b clear error when spectral is not installed (#1164)
• 8da9343 export project data (#1161)
• c420459 update project properties with registry apply (#1160)
• 1a03f32 validate +zip compression when indicated (#1162)
• 2e1642e names must be lowercase (#1158)
• 41f933b deprecate --max-actions in favor of --actions (#1157)