Add AlmaLinux OS scan support

[srbala]

What would you like to be added:
Add AlmaLinux OS as new RHEL variant along with CentOS

Why is this needed:
AlmaLinux is an alternative OS for CentOS as its long term supports ends by end of the year.

Additional context:
Source code level security issues of RHEL are applicable to AlmaLinux except vendor specific packages

[wagoodman]

Support for this was added in v0.16.0 of grype via anchore/syft#447 in syft 🎉 🌮

❯ grype version
Application:          grype
Version:              0.16.0
BuildDate:            2021-08-18T15:41:58Z
GitCommit:            01a77d5c451455e6125f26178db6fe2da2b7675d
GitTreeState:         clean
Platform:             darwin/amd64
GoVersion:            go1.16.7
Compiler:             gc
Supported DB Schema:  3

❯ docker pull almalinux
Using default tag: latest
latest: Pulling from library/almalinux
ba2c2d4a4d0c: Pull complete
Digest: sha256:7843d8cb9fb74495159ba58d27421cbc408d1760ce94b5bf54e8ebda83272199
Status: Downloaded newer image for almalinux:latest
docker.io/library/almalinux:latest

❯ grype almalinux:latest
 ✔ Vulnerability DB        [updated]
 ✔ Loaded image
 ✔ Parsed image
 ✔ Cataloged packages      [160 packages]
 ✔ Scanned image           [2 vulnerabilities]
NAME  INSTALLED  FIXED-IN  VULNERABILITY   SEVERITY
rpm   4.14.3               CVE-2021-20266  Medium
rpm   4.14.3               CVE-2021-3421   Medium