[Feature] support modified resnet structure used in oCLIP

[HannibalAPE]

Motivation

To support modified resnet structure used in oCLIP, which is also the official structure in CLIP.
Currently, I only implement CLIPResNet-50 when depth=50. CLIPResNet-101 would be implemented later.
We also provide a script for converting the parameter names of our models to MMOCR style.

For more information, please refer to oCLIP

Modification

Add a new ResNet structure, named as CLIPResNet in mmocr/models/common/backbones/clip_resnet.py

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[CLAassistant]

All committers have signed the CLA.