PMM Branded Logo in user invitation emails

We are continuously working towards a strong Percona brand market presence.

Currently, users can take advantage of user invite emails in PMM. This is where the default email template is still being used which does not come with the Percona Logo.

Therefore, we want to:

1. change logo to PMM

2. change footer to refer to PMM and Percona (Ask first marketing about copyright notice)

3. Add call to action part on alert email - https://perconadev.atlassian.net/browse/PMM-13657

4. Change mention of Grafana to PMM on emails

5. Change getting started doc url to TBD

To do that, we probably need a new design for the template.