(fix): Update path generated when creating LookML URL

[darapuk]

Pathlib by default removes the leading /, which leads to a trailing / being present in file_path after striping repo path.

The trailing / eventually causes the looker url to be incorrect.

I.e.:
base_url//file_path
to
base_url/file_path

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.

[github-actions]

Unit Test Results (build & test)

  96 files  ±0    96 suites  ±0   13m 58s ⏱️ - 11m 36s
686 tests ±0  627 ✔️ ±0  59 💤 ±0  0 ❌ ±0 

Results for commit 9e671b8. ± Comparison against base commit 2fc3a48.

[github-actions]

Unit Test Results (metadata ingestion)

       5 files  ±0         5 suites  ±0   1h 3m 39s ⏱️ + 2m 3s
   393 tests ±0     393 ✔️ ±0    0 💤 ±0  0 ❌ ±0 
1 809 runs  ±0  1 778 ✔️ ±0  31 💤 ±0  0 ❌ ±0 

Results for commit 9e671b8. ± Comparison against base commit 2fc3a48.

[rslanka]

LGTM!