[BUG] Strangeness with dataset.merge()

## 🐛🐛 Bug Report
To start with, awesome work getting the merge functionality implemented! I have used it for a while now and discovered a few issues with it:

### Text tensors are not merged
When two branches are merged, where both branches has the same tensors, some tensors are empty after merge. This applies to e.g. `htype="text"` and `htype="generic"`. See [example on colab here](https://gist.github.com/daniel-falk/623253501c4ef7dadd38a853ca532a57).

### UI shows errors during a merge
If using the ActiveLoop user interface while two branches are merging the dataset fails to load and there are error messages "Dataset is corrupted or does not exist".

### Exception about modification on read-only tensor during merge
While merging two branches I got this exception once. Rerunning with the same exact code a second time worked.
```
Error in sys.excepthook:
Traceback (most recent call last):
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/humbug/report.py", line 498, in _hook
self.error_report(error=exception_instance, tags=tags, publish=publish)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/humbug/report.py", line 244, in error_report
traceback.format_exception(
TypeError: format_exception() got an unexpected keyword argument 'etype'

Original exception was:
Traceback (most recent call last):
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/diff_commits.py", line 84, in
diff_commits()
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/click/core.py", line 1130, in __call__
return self.main(*args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/click/core.py", line 1055, in main
rv = self.invoke(ctx)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/click/core.py", line 1404, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/click/core.py", line 760, in invoke
return __callback(*args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/diff_commits.py", line 79, in diff_commits
ds_new.merge(f"debug4/diff-{hash1}-{hash2}-removed")
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/humbug/report.py", line 445, in wrapped_callable
return callable(*args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/invalid_view_op.py", line 22, in inner
return callable(x, *args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/iteration_warning.py", line 11, in inner
res = callable(x, *args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/core/dataset/dataset.py", line 1193, in merge
merge(self, target_id, conflict_resolution, delete_removed_tensors, force)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/merge.py", line 59, in merge
merge_common_tensors(common_tensors, dataset, target_ds, nodes, conflict_resolution)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/merge.py", line 289, in merge_common_tensors
merge_tensor_data(
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/merge.py", line 472, in merge_tensor_data
original_tensor.append(sample)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/invalid_view_op.py", line 22, in inner
return callable(x, *args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/core/tensor.py", line 377, in append
self.extend([sample], progressbar=False)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/util/invalid_view_op.py", line 22, in inner
return callable(x, *args, **kwargs)
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/core/tensor.py", line 306, in extend
self._write_initialization()
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/core/tensor.py", line 259, in _write_initialization
self.storage.check_readonly()
File "/Users/danielfalk/testprgm/sandbox/deeplake/versioning_tutorial/venv/lib/python3.10/site-packages/deeplake/core/storage/provider.py", line 153, in check_readonly
raise ReadOnlyModeError()
deeplake.util.exceptions.ReadOnlyModeError: Modification when in read-only mode is not supported!
```

### Removed samples are not removed after a merge
Data samples that are removed on a branch does not get removed when that branch is merged.

This might be a design decision, that when merging it is the current state of the source branch that is merged, not the changes/deltas on the branch. This "union" behaviour feels very unnatural for a "merge" and is not how it works in e.g. git. I could not find any documentation explaining this behaviour.

See [example on colab here](https://gist.github.com/daniel-falk/623253501c4ef7dadd38a853ca532a57).

### Merged commits are not visible in history
One of the main advantages with version control of the data is that I can look in the log and see what different changes people has done to the dataset. This does not really work as is now since a merge only creates a "merged ..." commit message, it does not show the commits that was done to other branches. This means that if using trunk-based development where the changes are always done on a feature branch, committed with a self-explaining commit message and then merged with master, there will not be any useful commit messages on the main branch, only "merge ..." messages. I think we would really need something like gitk etc. that shows the different commits on the branches that are merged.