perf: save auth requests for push and attach

[Wwwsylvia]

What this PR does / why we need it:
Add pull, push scope hints before calling Copy for oras push and oras attach.
This can potentially save 2 requests for each command.

oras push

oras push $myreg/$myrepo:$mytag --debug

Before

request #0: HEAD manifest digest - 401
request #1: POST token (scope: pull) - 200
request #2: HEAD manifest digest - 404
request #3: HEAD config ({}) - 404
request #4: POST config ({}) - 401
request #5: POST token (scope: pull, push) - 200
request #6: POST config ({}) - 202
request #7: PUT config ({}) - 201
request #8: PUT manifest tag - 201

After

request #0: HEAD manifest digest - 401
request #1: POST token (scope: pull) - 200
request #2: HEAD manifest digest - 404
request #3: HEAD config ({}) - 404
request #4: POST config ({}) - 202
request #5: PUT config ({}) - 201
request #6: PUT manifest tag - 201

oras attach

oras attach myreg/myrepo:mytag --artifact-type application/test foo --debug

Before

request #0: HEAD subject tag - 401
request #1: POST token (scope: pull) - 200
request #2: HEAD subject tag - 200
request #3: HEAD manifest digest - 404
request #4: HEAD config ({}) - 200
request #5: HEAD layer - 404
request #6: POST layer - 401
request #7: POST token (scope: pull, push) - 200
request #8: POST layer - 202
request #9: PUT layer - 201
request #10: PUT manifest tag - 201

After

request #0: HEAD subject tag - 401
request #1: POST token (scope: pull) - 200
request #2: HEAD subject tag - 200
request #3: HEAD manifest digest - 404
request #4: HEAD config ({}) - 200
request #5: HEAD layer - 404
request #6: POST layer - 202
request #7: PUT layer - 201
request #8: PUT manifest tag - 201

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1084

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov-commenter]

Codecov Report

Merging #1097 (a6a80b8) into main (2d6d36e) will increase coverage by 0.08%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1097      +/-   ##
==========================================
+ Coverage   79.99%   80.08%   +0.08%     
==========================================
  Files          56       57       +1     
  Lines        2914     2927      +13     
==========================================
+ Hits         2331     2344      +13     
  Misses        405      405              
  Partials      178      178              

Files Changed	Coverage Δ
cmd/oras/root/attach.go	82.64% <100.00%> (+0.74%)	⬆️
cmd/oras/root/push.go	75.70% <100.00%> (+0.70%)	⬆️
internal/registryutil/auth.go	100.00% <100.00%> (ø)

[shizhMSFT]

LGTM

[qweeah]

LGTM but this change can also be applied to manifest delete and blob delete

[TerryHowe]

LGTM.

[TerryHowe]

LGTM but this change can also be applied to manifest delete and blob delete

Follow up?

[qweeah]

LGTM but this change can also be applied to manifest delete and blob delete

Follow up?

Created #1104. @Wwwsylvia Do we still need to create the issue for copying?

[Wwwsylvia]

LGTM but this change can also be applied to manifest delete and blob delete

Follow up?

Created #1104. @Wwwsylvia Do we still need to create the issue for copying?

Created #1105.