Improve metric report formatting

[MarceloRobert]

Currently, the metrics email report is optimized for monospace text, but when viewed in the mailing list website, the numbers look out of place.

Consider using HTML to format them.

Example of metrics report: https://groups.io/g/kernelci-results/message/60416

How it looks in the mailing list:

[tales-aparecida]

Judging by today's Working Group meeting, I think we'll keep the report in plain-text with links pointing to React pages in the main Dashboard website

[tales-aparecida]

If I may steal this ticket, though, there is the suggestion for a new format:

COVERAGE
  --------
                      This week    Last week    Change
                      ─────────    ─────────    ──────
  Trees monitored     47           52           -5
  Checkouts           1,192        1,438        -246  (-17%)
  Builds              11,537       14,210       -2,673  (-19%)
  Tests               1,040,069    1,281,004    -240,935  (-19%)

  Note: Reduced activity is consistent with post-merge-window stabilisation.


  BUILD REGRESSIONS
  -----------------
  A "regression" is a newly detected failure (first occurrence).
  An "occurrence" is each subsequent hit of that same failure.

  Origin      Occurrences    New regressions
  ────────────────────────────────────────────
  maestro     155            1
  redhat      5              0
  microsoft   0              0
  ────────────────────────────────────────────
  Total       160            1


  TEST REGRESSIONS
  ----------------
  Origin      Occurrences    New regressions
  ────────────────────────────────────────────
  maestro     0              0
  redhat      0              0
  microsoft   0              0
  ────────────────────────────────────────────
  Total       0              0


  LAB ACTIVITY
  ------------
  10 labs reported results this week (unchanged from last week).

  Origin   Lab                   Builds   Boots    Tests      Change (tests)
  ──────────────────────────────────────────────────────────────────────────
  maestro  lava-collabora        0        6,141    572,028    -12,400  (-2%)
  maestro  lava-broonie          0        721      264,312    +8,100  (+3%)
  maestro  lava-kci-qualcomm     0        162      83,383     +1,200  (+1%)
  maestro  k8s-gke-eu-west4      0        0        743        -50  (-6%)
  maestro  k8s-all               64       0        151        +10  (+7%)
  maestro  lava-cip              0        727      85         0  (0%)
  maestro  lava-foundriesio      0        60       0          0  (0%)
  maestro  lava-kontron          0        111      0          0  (0%)
  maestro  lava-pengutronix      0        215      0          0  (0%)
  ti       opentest-ti           0        2,039    0          0  (0%)
  ──────────────────────────────────────────────────────────────────────────
  Total                          64       10,176   920,702