OpenMS and frequently mass shifts in Unimod

### Description of feature

@MaLLLiYA @timosachsenberg @jpfeuffer @daichengxin :

We have been analysing some of the datasets and we found some interesting unexpected PTMs (mass shits), most of them are here:

https://unimod.org/modifications_list.php?a=search&value=1&SearchFor=Unidentified+modification+of&SearchOption=Contains&SearchField=

```
1970 |   | Unknown:162 | Unidentified modification of 162.1258 found in open search | 162.125595 | 162.2267 | H(18) C(8) O(3)
```

Can we make sure these mods works in OpenMS? Also, Can you let us know @timosachsenberg how you can search with OpenMS tools for a delta mass when the mod is not defined on OpenMS?

Start by reviewing the Unimod search linked in the issue and the OpenMS tools relevant to searching for undefined delta masses. The issue is complete only when the handling of the listed modifications and the workflow for undefined mass shifts are clearly established; no repository files or tests are named.

Written by the indexing model from the issue text.