improve error message

[qweeah]

According to the error message guide (see PR), below works need to be done:

• improve error message when user mistakenly uses tag list command #1210
• improve error message when no tag or digest provided #1211
• improve error message when pushing a manifest without media type #1212
• improve error message when attaching with invalid spec option #1213
• improve error message when attaching with invalid input #1214
• improve error message when pushing with invalid annotation flags #1215
• improve error message when namespace is not specified in the reference of Dockerhub artifacts #1216
• improve error message when invalid options given when pushing #1217
• improve error message when registry credential config is not valid #1236

All issues might change since the guideline hasn't got merged yet.

[amands98]

Are you currently working on this task, or should I handle it? // @qweeah @yizha1

[qweeah]

@amands98 Yes I am working on it.

[amands98]

Can I help you ?

[qweeah]

@amands98 Thanks for volunteering. #1217 is still not taken but it's planned in the upcoming release v1.2.0. Considering the time urgency, I suggest to commit on future items, e.g. #1066

[qweeah]

Closing as all sub-issues are completed