github: Use shared Renovate config

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

Use shared Renovate config in https://github.com/ni/python-renovate-config

Switch back to .json file extension. The Renovate docs say

Renovate supports JSONC for .json files and any config files without file extension (e.g. .renovaterc). We also recommend you prefer using JSONC within a .json file to using a .json5 file if you want to add comments.

Why should this Pull Request be merged?

Single-source Renovate config for Python projects.

What testing has been done?

Tested in https://github.com/bkeryan/nitypes-python

[github-actions]

Test Results

    34 files  +    12      34 suites  +12   56m 51s ⏱️ + 25m 40s
 2 515 tests ±     0   2 145 ✅ ±     0    370 💤 ±    0  0 ❌ ±0 
44 838 runs  +21 369  38 426 ✅ +18 163  6 412 💤 +3 206  0 ❌ ±0 

Results for commit 2409b32. ± Comparison against base commit 31b4881.