cli: add config and images command

Extends the existing zot CLI to add commands for listing all images and
their details on a zot server.
Listing all images introduces the need for configurations.

Each configuration has a name and URL at the least. Check 'zot config
-h' for more details.

The user can specify the URL of zot server explicitly while running the
command or configure a URL and pass it directly.

Adding a configuration:
zot config add aci-zot <zot-url>

Run 'zot config --help' for more.

Listing all images:
zot images --url <zot-url>

Pass a config instead of the url:
zot images <config-name>

Filter the list of images by image name:
zot images <config-name> --name <image-name>

Run 'zot images --help' for all details

- Stores configurations in '$HOME/.zot' file

Add CLI README

errors/errors.go

@@ -3,27 +3,35 @@ package errors
 import "errors"
 
 var (
-	ErrBadConfig           = errors.New("config: invalid config")
-	ErrRepoNotFound        = errors.New("repository: not found")
-	ErrRepoIsNotDir        = errors.New("repository: not a directory")
-	ErrRepoBadVersion      = errors.New("repository: unsupported layout version")
-	ErrManifestNotFound    = errors.New("manifest: not found")
-	ErrBadManifest         = errors.New("manifest: invalid contents")
-	ErrUploadNotFound      = errors.New("uploads: not found")
-	ErrBadUploadRange      = errors.New("uploads: bad range")
-	ErrBlobNotFound        = errors.New("blob: not found")
-	ErrBadBlob             = errors.New("blob: bad blob")
-	ErrBadBlobDigest       = errors.New("blob: bad blob digest")
-	ErrUnknownCode         = errors.New("error: unknown error code")
-	ErrBadCACert           = errors.New("tls: invalid ca cert")
-	ErrBadUser             = errors.New("ldap: non-existent user")
-	ErrEntriesExceeded     = errors.New("ldap: too many entries returned")
-	ErrLDAPEmptyPassphrase = errors.New("ldap: empty passphrase")
-	ErrLDAPBadConn         = errors.New("ldap: bad connection")
-	ErrLDAPConfig          = errors.New("config: invalid LDAP configuration")
-	ErrCacheRootBucket     = errors.New("cache: unable to create/update root bucket")
-	ErrCacheNoBucket       = errors.New("cache: unable to find bucket")
-	ErrCacheMiss           = errors.New("cache: miss")
-	ErrRequireCred         = errors.New("ldap: bind credentials required")
-	ErrInvalidCred         = errors.New("ldap: invalid credentials")
+	ErrBadConfig               = errors.New("config: invalid config")
+	ErrRepoNotFound            = errors.New("repository: not found")
+	ErrRepoIsNotDir            = errors.New("repository: not a directory")
+	ErrRepoBadVersion          = errors.New("repository: unsupported layout version")
+	ErrManifestNotFound        = errors.New("manifest: not found")
+	ErrBadManifest             = errors.New("manifest: invalid contents")
+	ErrUploadNotFound          = errors.New("uploads: not found")
+	ErrBadUploadRange          = errors.New("uploads: bad range")
+	ErrBlobNotFound            = errors.New("blob: not found")
+	ErrBadBlob                 = errors.New("blob: bad blob")
+	ErrBadBlobDigest           = errors.New("blob: bad blob digest")
+	ErrUnknownCode             = errors.New("error: unknown error code")
+	ErrBadCACert               = errors.New("tls: invalid ca cert")
+	ErrBadUser                 = errors.New("ldap: non-existent user")
+	ErrEntriesExceeded         = errors.New("ldap: too many entries returned")
+	ErrLDAPEmptyPassphrase     = errors.New("ldap: empty passphrase")
+	ErrLDAPBadConn             = errors.New("ldap: bad connection")
+	ErrLDAPConfig              = errors.New("config: invalid LDAP configuration")
+	ErrCacheRootBucket         = errors.New("cache: unable to create/update root bucket")
+	ErrCacheNoBucket           = errors.New("cache: unable to find bucket")
+	ErrCacheMiss               = errors.New("cache: miss")
+	ErrRequireCred             = errors.New("ldap: bind credentials required")
+	ErrInvalidCred             = errors.New("ldap: invalid credentials")
+	ErrInvalidArgs             = errors.New("cli: Invalid Arguments")
+	ErrInvalidFlagsCombination = errors.New("cli: Invalid combination of flags. Add --help flag")
+	ErrInvalidURL              = errors.New("cli: invalid URL format")
+	ErrUnauthorizedAccess      = errors.New("cli: unauthorized access. check credentials")
+	ErrCannotResetConfigKey    = errors.New("cli: cannot reset given config key")
+	ErrConfigNotFound          = errors.New("cli: config with the given name does not exist")
+	ErrNoURLProvided           = errors.New("cli: no URL provided in argument or via config. see 'zot config -h'")
+	ErrIllegalConfigKey        = errors.New("cli: given config key is not allowed")
 )