[17.0][IMP] dms: Implement index_content and create dms_indexation mo…

[dakshesh-sttl]

…dule

[victoralmau]

Same comments as indicated in #366 (review)

[victoralmau]

Some comments:

• Check pre-commit errors.
• Modify the PR title, e.g.: [17.0][ADD] dms_indexation: New module
• Unify all changes in a single commit ([17.0][ADD] dms_indexation: New module for example).
• Modify the module icon with the existing dms icon + attachment indexation combination (or if you prefer, you can use the one for default).
• You can add files to the readme folder to describe the module and how to use it.
• You are adding more stuff than necessary (the attachment_indexation module already takes care of that), I think the method should be very similar to https://github.com/odoo/odoo/blob/583e785fc6e2acababa5865a6e0e8e71f3df8a49/odoo/addons/base/models/ir_attachment.py#L384.