[FIX] website_blog: prevent losing search params

Before this commit, search criteria could be lost when a visitor added a
new search criteria on blogs. This commit solves this problem.

Steps to reproduce the issues (with activate the sidebar):
- Go to the /blog
- Click on the adventure tag
- Select a month in the date filter

=> The adventure tag is lost.

- Go to the /blog
- Select a month in the date filter
- Click on the adventure tag
- Remove the date filter

=> The adventure tag is lost.

- Go to the /blog
- Select a month in the date filter
- Search for the blogs containing the word "heli"

=> The date filter is lost.

task-3058239

Part-of: odoo/odoo#105462