Add the ContentLengthHasBeenSet() method

[yariks5s]

Issue #, if available:
ClickHouse/ClickHouse#99971

Description of changes:
This change is needed for the PR: . That PR fixes a case where ClickHouse can receive a file that does not have a Content-Length header in the HEAD request response, and therefore these files are skipped because their size was zero (default value). Required for ClickHouse/ClickHouse#99971

Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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