Projects page: Add a separate filter for Project Level

Community & Support: [LinkedIn Group](https://www.linkedin.com/groups/14656108/) · [Slack #project-nest](https://owasp.slack.com/archives/project-nest)

Active project leaders: Arkadii Yakovets -- [GitHub](https://github.com/arkid15r/) · [LinkedIn](https://www.linkedin.com/in/arkid15r/) · [Slack](https://owasp.slack.com/team/U060W3NKLTF); Kate Golovanova -- [GitHub](https://github.com/kasya/) · [LinkedIn](https://www.linkedin.com/in/kate-golovanova/) · [Slack](https://owasp.slack.com/team/U07PWB1JZ6Z)

[Contributing](https://github.com/owasp/nest/blob/main/CONTRIBUTING.md) · [Code of Conduct](https://github.com/owasp/nest/blob/main/CODE_OF_CONDUCT.md) · [GSoC Mentors](https://github.com/owasp/nest/blob/main/MENTORS.md)

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**Is your feature request related to a problem? Please describe.**
I am always frustrated when I come to the Nest Projects page and I need to see FlagShip or Lab projects. While an ascending/descending sorting exists it is still difficult to find what you are looking for. It would also help to **see how many projects OWASP has on each level**

**Describe the solution you'd like**
A separate filter on top of the page by projects level showing the number of projects of that level in brackets like this:
(x) All Projects (459)
( ) Flagship Projects (15)
( ) Production Projects (12)
( ) Lab Projects (33)
( ) Incubator Projects (259)

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Are you going to work on implementing this?**

- [ ] Yes
- [x] No

**Additional context**
This will enable and easy way to see and search the projects of the specific maturity level