yaml storage, gcloud create

• registry apply --yaml option to store artifacts as yaml
• registry config configurations create --gcloud option uses gcloud settings
• improved help for various commands
• builds now use go 1.20

Changelog

• 11486e8 Remove code needed for Go versions below 1.18 (#1201)
• 995ef9f allow nil bodies in create resource endpoints (#1202)
• c601ea6 switch builder to golang:1.20-bullseye (#1200)
• dbcf45d set builder to golang:1.20.4, remove toybox (#1197)
• 46787a5 improve apply and config command help (#1194)
• 33b2bb5 ensure migrate artifacts is idempotent (#1195)
• 391037f rewrite migrateArtifactsToRevisions to avoid dups (#1193)
• d52c911 Update setup-go action to v4 (#1190)
• 74de29d Update Go version to 1.20 (#1187)
• 074c047 Indent usage string, available commands, and available plugins (#1186)
• cd48182 Only print Available Plugins when the list is not empty. (#1185)
• 7af9790 add --gcloud flag to registry create (#1184)
• 9b8f9a4 Remove "All Rights Reserved." from copyright (#1183)
• f3ddf3b support both serialized protos and YAML (#1181)
• 8dab302 default version to empty, not latest (#1178)
• 78104e2 registry apply --yaml for artifacts (#1174)
• 0fef98b remove defaultTestServer conflict (#1173)
• e9cc44a use consistent yml extensions (#1171)
• 487c59d fix disable flag input (#1170)
• a07cc36 mega test coverage (#1169)