Adding issue and merge request templates

<!--

* Use this issue template for reporting a new UX bug.

-->

### Summary

**Summarize the bug encountered concisely.**

### Steps to reproduce:

**How one can reproduce the issue - this is very important.**

1. Step 1

2. Step 2

3. ...

### What is the current bug behavior?

**What actually happens.**

### What is the expected behavior?

**What you want to see instead**

## Relevant logs and/or screenshots

**Do you have screenshots? Attach them to this ticket please.**

/label ~tor-ux ~needs-investigation ~bug

/assign @nah

<!--

* Use this issue template for reporting a new bug.

-->

### Summary

**Summarize the bug encountered concisely.**

### Steps to reproduce:

**How one can reproduce the issue - this is very important.**

1. Step 1

2. Step 2

3. ...

### What is the current bug behavior?

**What actually happens.**

### What is the expected behavior?

**What you want to see instead**

### Environment

**Which operating system are you using? For example: Debian GNU/Linux 10.1, Windows 10, Ubuntu Xenial, FreeBSD 12.2, etc.**

**Which installation method did you use? Distribution package (apt, pkg, homebrew), from source tarball, from Git, etc.**

### Relevant logs and/or screenshots

/label ~bug

## Merge Info

<!-- Bookkeeping information for release management -->

- ### Related Issues

  - tor-browser#xxxxx

  - tor-browser-build#xxxxx

  - etc

- ### Backport Timeline

  - [ ] **Immediate** - patchsets for critical bug fixes or other major blocker (e.g. fixes for a 0-day exploit) OR patchsets with trivial changes which do not need testing (e.g. fixes for typos or fixes easily verified in a local developer build)

  - [ ] **Next Minor Stable Release** - patchset that needs to be verified in nightly before backport

  - [ ] **Eventually** - patchset that needs to be verified in alpha before backport

  - [ ] **No Backport** - patchset for the next major stable

- ### Upstream Merging

  - [ ] Merge to `base-browser` - typically for `!fixups` to patches in the `base-browser` branch, though sometimes new patches as well

    - **NOTE**: if your changeset includes patches to both `base-browser` and `tor-browser` please please make separate merge requests for each part

- ### Issue Tracking

  - [ ] Link resolved issues with appropriate [Release Prep issue](https://gitlab.torproject.org/groups/tpo/applications/-/issues/?sort=updated_desc&state=opened&label_name%5B%5D=Release%20Prep&first_page_size=20) for changelog generation

## Change Description

<!-- Whatever context the reviewer needs to effectively review the patchset -->

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