Add new auth for tencentcloud cos backend

[SevenEarth]

Add more authentication method for COS backend.

Target Release

1.19.x

Draft CHANGELOG entry

ENHANCEMENTS

• Support shared_credentials_dir, profile authentication method
• Support cam_role_name authentication method
• Updated documentation for TencentCloud cos backend

[hashicorp-cla-app]

All committers have signed the CLA.

[hashicorp-cla-app]

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[SevenEarth]

@crw Hello, I've signed the CLA, Please review this pr. thanks

[SevenEarth]

@crw Hi, I've signed the CLA, Please review this pr. thanks

[jbardin]

cc @likexian, listed as the codeowner for this backend

[SevenEarth]

Hi @likexian, pls help to review my PR. 3q.

[likexian]

LGTM

[SevenEarth]

@jbardin Hi, could you please take a look at this pr, thanks?